I couldn't load Miroslav Philharmonic (32-bit only) in neither Sonar, nor in MC7 (both 64-bit). DXi version is listed, but greyed out and I get en error that the synth is not correctly installed, which isn't true, because it runs correctly as a standalone and in Reaper. VSti x32 version is not even listed, although a correct x32 plugins path is added to the VST locations box. What can cause such an error? How to fix this?

Old 32bit IK plug-ins usually require running the DAW as administrator. Unless wrapped as a VST, it is strange a 64bit DAW even sees a 32bit DirectX plug-in.

scook
Old 32bit IK plug-ins usually require running the DAW as administrator. Unless wrapped as a VST, it is strange a 64bit DAW even sees a 32bit DirectX plug-in.

Thank you for your reply! I'll try to be more descriptive.
The error:

 
I also installed a VSTi version, but Sonar does not find it at all.
 


 
I rescanned plugins, it didn't help.
 

 
Sonar only sees a DXi version
 

 
but it is greyed out in the plugin layout manager.
 

 
Any thoughts?

Run Sonar as administrator and then rescan. Note that you will be able to use MP in that mode only and there are still quite some glitches.
 
There was big discussion in the Software section, the best advise is to get ST 3 (can be SE, but not free). If you do this today or tomorrow, you still can participate in the current action and get 5 extensions for free...

I had the same issue with SampleTank but when I opened Sonar as admin I was able to get it to work.  I had made a folder in the C:\Program Files\Cakewalk\VstPlugins called SampleTank then put the SampleTank2.x.dll in that folder.  When I started Sonar as admin it saw the .dll and then SampleTank was available.  Incidentally I had to set up Sonar to always start as admin because I couldn't get SampleTank to load unless I opened as admin.......hope this helps because your issues looks like it is exactly like what I was going thru.

Also try inserting the synth as split audio/midi, NOT as a Simple Instrument Track

I don't think you will ever succeed in running a 32bit DirectX plug-in a Cakewalk DAW without a DX-to-VST wrapper and then the plug-in will show up in the VST2 list. WRT the actual VST plug-in not appearing in the list, did you try running a VST reset. Here is how http://www.cakewalk.com/S...ed-for-Upgraders 
 
And yes, as the other have said, run SONAR as administrator.

If you have Sampletank 3 you can integrate the sounds of Miraslav Into Sampletank.
You install through the legacy Instruments section
The same goes for Samplemoog.Sampletron and Sonic Synth.
They will then work as Sampletank 3 and Is the same for Knobs and all.Just a different Layout.

I've never understood the problems people have had with the 32-bit IK VIs.  I ran Sampletank 2.5 for years under 64-bit Sonar (Bitbridge only) and, well, it just worked.  I also had Miroslav Phil and Sonik Synth, but used them as libs within Sampletank (so  only had Sampletank running).
 
Of course, I've always registered the programs using the standalones (not the plugins), done a Reset/Rescan of VSTs after every change, and "Run as Admin" with all installs and when running applications.  Seems to me one or more of these has got to be the key ingredient(s) with using the IK 32-bit stuff successfully.
 
I have Sampletank 3 now, so no more Bitbridge, and I've imported the older libs.  I still follow the old steps out of habit, though, and can't say I've run into any glitches with the newer version either.

As the others have noted, running as administrator and then re-scanning plug-ins usually does the trick. If not, a VST reset and rescan can help:
 
1) Go into the Plug-in Manager (Utilities>Cakewalk Plug-in Manager)
2) Click Options
3) Select both boxes (Re-scan failed and existing plug-ins),
4) Click Reset All, and then OK
5) Click Scan VST Plug-ins
6) Go back into Options after doing this, and uncheck both boxes.