It's easy to work around but strange behavior none the less....
 
Miroslav Philharmonic is a 32-bit VST2 plugin.  On my setup it loads & runs right away as a standalone program, but when inserted into a SONAR project it causes the project to freeze during loading the file (the loading activity icon just spins and spins and nothing ever loads.)  However, load any other project (even a midi loop) first then the Philharmonic-containing file can be loaded and opens right away.  So you see I have and easy work-around, but it's a bit of a head scratcher.
 
Some things I've tried:
-- Un-install & re-install Philharmonic plug-in
-- Install 32-bit version of X3 and try opening projects (they fail with an error that kills X3!)
-- re-scan VSTs (in 64-bit X3 all is OK, in 32-bit a warning that Philharmonic may be unstable)
-- run 64-bit X3 as administrator (no change in behavior)
 
I just wonder if anyone else has had any trouble with it or if maybe there're bugs in Philharmonic I don't know about.

If you are loading the 32 bit version in the 64 bit version of SONAR then it is running under bitbridge. If they have a 64 bit native version that is the best option. There is a problem with Bitbridge where VST's that have > 1Mb of plugin state can hang.

Sadly there are no 64 bit version of any of the IKMultimedia synths yet though Sampletank 3 is supposed to be released soon.

I have them running fine on my x64 system that has gone from Vista to Win 7 and now Win 8.1

Earlier it worked best with jBridge but under Win8.1 and Sonar X3d it works best under Bitbridge.

Aha! Thanks Noel.
Too bad they don't have a 64-bit version, it seems like an older product in the "milking for cash" phase.

No. All the iK M synths are very good products and have very good sound libraries.

Make sure the automatic library rescan option is disabled. Click on "Prefs" in the lower-right corner of the main panel, then set the "Relist on startup" option to OFF (click on "ON" to turn it "OFF").

Been using Philharmonik for a while on Sonar X1, 2 and 3 without any issues. Yes it's 32 bit and I don't believe we'll see a 64 bit version any time soon!  IK has been promising a 64 bit version of Sample Tank for ages and keep on changing the release date.  But I still love Philharmonik!

I just upgraded to X3 from X1, and boy was I upset to discover that none of my templates opened, and very few of my projects opened!  Same exact symptoms you described at the start of this thread.  Thankfully, it didn't take me long to narrow down the problem was related directly to the Philharmonic VST.  It was a serious relief, because it was starting to look like X3 wasn't going to work for me AT ALL. 
 
I opened up a project in X1 to remove the references to Philharmonic and saved without, and then X3 opened the project without a problem.  That's when I discovered my Philharmonic.dll wasn't even in the 32-bit VST folder (because I'm on a new computer), so I figured the problem was because it was MISSING.  Moved the .dll over and tried opening the original project in X3... still no luck.  I only found this thread after I figured out the problem, so it's nice to have the diagnosis validated.  I tried your work-around, and that didn't work either.   
 
Further symptoms of this issue: during the period when Sonar X3 SHOULD have opened the project but the loading activity icon just spins, it starts causing erratic behavior of my PreSonus fader port control surface: lights start blinking and the motorized fader sputters.
 
For now, it appears that if I want to use my Philharmonic, I'll just have to stay inside X1.  Not that big of deal, and certainly NOT a deal-breaker for using X3.  I can live without it going forward, now that I have many other orchestra sample libraries to cover that gap.
 
Mostly glad to discover I'm not the only person with the issue, and to know I can continue to use X3 for all my future projects.  It just means I'll have to clean the Philharmonic out of all my templates.

Just wondering, have you completed the activation/registration for Philharmonik yet? I've had issues with those synths, where having an unregistered plugin would either freeze your DAW or load a modal dialog that was somehow hidden behind the DAW. If you haven't been through the activation yet, run Miroslav as administrator in standalone mode and activate it.
 
Once you can load it in standalone without getting through activation, see how it behaves inside Sonar.

I have just purchased Miroslav Philharmonic from I K Multimedia and installed it on my computer now using Windows 10 After a bit of a problem I eventually got it to work in stand alone mode but can't for the life of me get it to work as a VST within Sonar Platinum I have uninstalled and reinstalled the download file on numerous occasions and transferred the file to various locations including Program Files Shared VSTs, within my existing I K Multimedia folder and even direct into my Cakewalk folder. I have never experienced this problem with other IK Multimedia VSTs such as Sample Tank or Amplitube so don't understand why this should be any different. Would be interested to hear whether anyone else has experienced a similar problem and how to overcome it