Weird Behavior with Miroslav Philharmonic VST

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.

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.

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").

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.

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 

Had the same problem. Miroslav is just Sample Tank 2 with dedicated skin and orchestra samples. You may download free ST2 from IK site (this time it should be seen as a new Sonar plugin) and then in prefs point to the folder where you keep Miroslav samples.  You will have fully functional Miroslav but with basic ST2 skin.