** WARNING - THIS POST WAS WRITTEN BY A REALLY PISSED OFF USER **
 
Before you reply with something like "Your thread title should be more helpful", that is my point.
 
I have put off upgrading from X3e for years because I worried it would not go smoothly and I would lose days of work time, and turned out I was right. When installing Professional from Command Center, after some downloading time I get the error "Sorry, a problem occurred" with a suggestion to contact support. So very helpful.
 
I had a trial version of Sonar Professional on the machine already, so I followed the instructions on performing a clean install by removing registry folders etc., but I still get the same error. I am leaving X3e on my machine, so I said No to All when it asked me if I wanted to removed shared files.
 
And since when has Cakewalk resorted to email support only? Since I can't be at the DAW workstation all day long, email only means this process is going to take days. Which is exactly why I have put off upgrading for so long. 
 
So, Cakewalk support team: Here was my experience:
1. Spent a bunch of money on Sonar Professional
2. Got Command Center installed
3. Tried to install Sonar Professional. Two buttons: "Install" and "Install All". Huh? Install All what? Well, I don't want some sort of partial install, so I guess I'll choose "Install All". "A problem occurred". A message popped up briefly saying something about a problem with downloaded files, and that I should click the Download button to get the rest of them. Or something like that. The message disappeared before I could catch it all. And oh.... WHAT DOWNLOAD BUTTON????
4. Went to Control Panel to uninstall my trial version of Sonar Professional
5. Sonar Professional was not listed in Program in Control Panel
6. Very confused now, started poring through support site
7. Found something that said I should uninstall from Command Center
8. Could not find uninstall option in Command Center
9. Went back to support pages, finally learned I need to RIGHT-CLICK the program entry to uninstall. NOT INTUITIVE!
10. Uninstalled Sonar Professional
11. Tried install again
12. Went to the support page to contact tech support
13. Discovered it was email only. I get 90 minutes a day at the DAW, so email is not practical
14. Looked through FAQ docs, found article on performing a clean install
15. Followed clean install instructions, including removing registry folders, etc.
16. Tried install again
17. "A problem occurred"
18. Returned to support page, filled out form for email support. Congrats, Cakewalk, I am now entirely pissed off.
 

Update:
 
Everything started installing correctly when I cleared more space on my drive. Cakewalk, you could have told me this. Pretty simple cause to report to me. 
 
Also, "Install All", which doesn't really tell me anything, ended up running a dozen or so plug-in things, most of which I had no idea what they were. So I just installed them. I doubt I will ever use them.
 
Cakewalk, you need to be much better in explaining to users what they are installing. "Install All" is confusing. This endless series of plug-in installs is confusing and stressful. Help us out here.

I can see why you got pizzed, most of us would be too. 
 
But your issue was probably a glitch in the download  which happens with all software downloads. 
Then you might be not up to date with "How things work" around here and didn't understand Command Centre and used the infamous Down Load all button, which most of us are Pizzed because it should be called download some of the stuff maybe button.. To enjoy Sonar fully you should stop by this forum more often as this would have kept you up to date on "How things work" 
Or even don't be afraid to ask "before" you make any changes. 
Hope it's all running now. 

jkoseattle
Everything started installing correctly when I cleared more space on my drive. Cakewalk, you could have told me this. Pretty simple cause to report to me. 

 
"A problem occurred" could be for a variety of reasons other than lack of hard drive space. In the CCC, you can see how much space each component to be installed requires. (As a side note, it's recommended to leave at least 10% of your C: drive space free so take that into account.)

You can reclaim drive space if you delete the contents of the Command Center download folder after installing an update. You can find it by clicking the gear in the upper right hand corner and selecting paths. The default location is C:\ProgramData\Cakewalk\Command Center\Downloads.
 
Rocky

Anderton

jkoseattle
Everything started installing correctly when I cleared more space on my drive. Cakewalk, you could have told me this. Pretty simple cause to report to me. 

 
"A problem occurred" could be for a variety of reasons other than lack of hard drive space. In the CCC, you can see how much space each component to be installed requires. (As a side note, it's recommended to leave at least 10% of your C: drive space free so take that into account.)

ccc should check that there's enough hd space available! 2 lines of code!

This is a good example of a time when you have have to take a deep breath and calm down. Things are usually not as bad as they seem at first. When I have an issue like this I tend to walk away and pour a cup before returning to walk through the issue with a checklist. Hard it is to see, when panicked you are.

ampfixer
This is a good example of a time when you have have to take a deep breath and calm down. Things are usually not as bad as they seem at first. When I have an issue like this I tend to walk away and pour a cup before returning to walk through the issue with a checklist. Hard it is to see, when panicked you are.

I know, you're right. What I didn't add was that my rant came after a couple days of already having done that. 
 

"Cactus Music"
To enjoy Sonar fully you should stop by this forum more often as this would have kept you up to date on "How things work" 

 
"You should just know" is not a good customer relationship strategy. "People who live in this town just know that exit 29 is a dead-end, so we don't need signs."
 
Anyway, thanks for the replies everyone. I removed a bunch of stuff and got everything installed. And the #1 reason I decided to upgrade, the improved PRV Track Pane, is a thing of beauty!

This forum is the best place to learn about Sonar and how to deal with issues. It would be a good idea to check in to this forum regularly.
 
I would highly highly recommend having more disk space available, although I don't see that you listed what size drives you have.   Cheers!