One odd thing is that I can get the problem loops to play at high bpm (above 190) but they'll hang Sonar below.

I followed your instructions to the letter, scook, and re-installed Dim Pro and the expansion packs, but it's still the same. Then, today, I downloaded Dim Pro and the Expansion packs again without any AV running (after uninstalling them first), and re-installed them and it's still the same. So, I give up. Thanks for trying to help, though. I appreciate your efforts.

Not a surprise, the files used previously were good. If you would like, we can go step by step with a program that is throwing errors to see where the problem lies but I would recommend calling customer support.
 
If the error is a dialog with the title "Multisample Not Found" note the sfz file name in the dialog. Search for the sfz file in the dialog. if found, report the full path. Also provide the value in "Multisamples folder", if any for the registry keys:
HKEY_LOCAL_MACHINE\SOFTWARE\Cakewalk Music Software\dp
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Cakewalk Music Software\dp
 
If the error opens notepad, post the contents of the text here. This type of error also creates an sfzlog.txt in "C:\Program Files\Cakewalk\Dimension Pro" assuming a default install.

>If the error is a dialog with the title "Multisample Not Found" note the sfz file name in the dialog.
 
One thing I've just noticed: The error message I get is, e.g., "HH_bonusbeats_100_04.rx2 not found." Is it supposed to be an .rx2 file? Shouldn't it be an .sfz file? Or is the .rx2 a slice of the .sfz, or something?

Also, as I noted earlier, none of the .sfz files in the C:\Program Files\Dimension Pro\Multisamples\70 - Drum Loops folder in Windows Explorer appear in the Program Browser of Dimension Pro, and vice versa - none of the files in the Program Browser of Dimension Pro appear in my Multisamples folder.

Another thing which seems strange to me is that besides the Multisamples folder in C:\Program Files\Dimension Pro, there is another Multisamples folder just sitting on the C:\ drive (i.e. C:\Multisamples). C:\Multisamples has only 15 folders, compared to the C:\Program Files\Dimension Pro folder which has 39 folders. They are the same folders, though, just not all of them.

I made sure that none of these existed before I re-installed, but they have re-appeared exactly as before.

I might call tech support, although I'm in Australia so I assume it will be an expensive call. Also, I'm really only interested in one file, which is HH_BonusBeats_90_01, which I used in one of my songs a couple of computers ago, when the file was actually working for me. I think it hasn't worked since the X1 upgrade.

Maybe some of this information gives a clue to the issue?

If you are only interested in HH_BonusBeats_90_01 maybe this would be a good place to start. Would you like to load it and go through the process described in #33?

I can't load it because it doesn't appear in the Program Browser of Dimension Pro.
 
And for those that do appear, all I get is the error message: Multisample Not Found. And in the error message it lists an rx2 file, not an sfz file.

Luke73
 
Also, as I noted earlier, none of the .sfz files in the C:\Program Files\Dimension Pro\Multisamples\70 - Drum Loops folder in Windows Explorer appear in the Program Browser of Dimension Pro, and vice versa - none of the files in the Program Browser of Dimension Pro appear in my Multisamples folder.

 
 
There are two categories of files that you have to keep separate in your mind : Multisamples and Programs
 
1. Multisamples :
 
   - reside in the Multisamples folder (wherever you put it  --> you have the choice)
 
   - this folder contains the *.sfz's and their samples (wav, flac, etc)
 
2. Programs :
 
   - reside in C:\ProgramData\Cakewalk\Dimension Pro\Programs   (I hope this is right, I'm not at my daw)
 
   --> you don't get the choice to put these elsewhere
 
   - this folder contains the program files  *.prog's
   - each program contains DimPro settings and pointers to the sfz and sample files for its Elements.
 
What shows up in DimPro's browser is only what is found in the Programs folder.
 

Luke73
 
Another thing which seems strange to me is that besides the Multisamples folder in C:\Program Files\Dimension Pro, there is another Multisamples folder just sitting on the C:\ drive (i.e. C:\Multisamples). C:\Multisamples has only 15 folders, compared to the C:\Program Files\Dimension Pro folder which has 39 folders. They are the same folders, though, just not all of them.
 

 
This folder appears for several reasons and I keep having to delete it since it only duplicates what is found elsewhere.  May be from Dimension LE ( ? not sure) or DSF sample packs (for some reason they go both here and where you tell them to) and possibly other sources.  Just make sure they're duplicates before deleting the folder.

You can look at the contents of a program file with Notepad.  It'll be mostly garbage, but you can see the references to the sfz files, which may tell you where DimPro is looking for them.
 
 

There are two categories of files that you have to keep separate in your mind : Multisamples and Programs
 
1. Multisamples :
 
   - reside in the Multisamples folder (wherever you put it  --> you have the choice)
 
   - this folder contains the *.sfz's and their samples (wav, flac, etc)
 
2. Programs :
 
   - reside in C:\ProgramData\Cakewalk\Dimension Pro\Programs   (I hope this is right, I'm not at my daw)
 
   --> you don't get the choice to put these elsewhere
 
   - this folder contains the program files  *.prog's
   - each program contains DimPro settings and pointers to the sfz and sample files for its Elements.
 
What shows up in DimPro's browser is only what is found in the Programs folder.
 
Thanks for the clarification. I thought it was something like this, but wasn't sure. It's the programs in the Program Browser of Dimension Pro which are giving me the error message of Multisample Not Found when I try and load them (this is only for the Expansion Pack 2>Grooves folder programs). However, the error message says that the file that isn't found is an .rx2 file (which has the same name as the program). I assume that the .rx2 file is an element of the program (?). However, when I search for these .rx2 files on the C: drive, they are not there. 

Not sure where or when hh_bonus_beats_90_01 was added. My DimPro installation goes back to the original release. When moving to a new machine, I copied over some libraries. Specific library issues are difficult to trace on my setup. hh_bonus_beats_90_01 is not part of Expansion Pack 2 on my system. The program is under "19 - Drum Grooves". I don't remember is this is a library copied from my old machine or not but it contains flac files so this would indicate it is a fairly recent addition.
 
FWIW, the Expansion Pack > Grooves > Hip Hop Breaks are rx2 files. DimPro can load and play them too. The process for diagnosing those errors should be similar to sfz files. Search for the rx2 file, report the path if found and the registry key info.

Luke73
It's the programs in the Program Browser of Dimension Pro which are giving me the error message of Multisample Not Found when I try and load them (this is only for the Expansion Pack 2>Grooves folder programs). However, the error message says that the file that isn't found is an .rx2 file (which has the same name as the program). I assume that the .rx2 file is an element of the program (?). However, when I search for these .rx2 files on the C: drive, they are not there. 

The programs using REX files are named for the REX file in element 1. The default location for the REX drum loops is "C:\Program Files\Cakewalk\Dimension Pro\Multisamples\72 - REX Drum Loops". The HH files are in a subdirectory called "Hip Hop Beats".