I just tried to open a project from September and it freezes Sonar with that faded white screen. I get the message "SONARPLT.exe has stopped working. Under View Problem Details is the following:
 
Problem signature:
  Problem Event Name:    APPCRASH
  Application Name:    SONARPLT.exe
  Application Version:    21.11.0.25
  Application Timestamp:    566ebb2c
  Fault Module Name:    SONARPLT.exe
  Fault Module Version:    21.11.0.25
  Fault Module Timestamp:    566ebb2c
  Exception Code:    c0000005
  Exception Offset:    0000000000b6ff92
  OS Version:    6.1.7601.2.1.0.768.3
  Locale ID:    1033
  Additional Information 1:    9a20
  Additional Information 2:    9a20cad8b106b0d3fb0ba50c5c971bfc
  Additional Information 3:    b8ff
  Additional Information 4:    b8ffa2785e9f8e1df10c67aba64eb4bf
 
 
Nothing on my system has changed since the project was last saved other than Sonar updates.

Upload a minidump for the crash and we can take a look at it.

I'm having a very similar issue right now. 
How do I upload it? 
 
Everytime I click "send" on the fault reporter it says it can't connect. (not an internet issue). 
 
But this is a big problem for me right now. 

Same issue just starting a new project and loaded one synth addictive keys.....immediately got the error

Welcome to the forum.
 
if its a new project that is crashing by only adding ADD Keys, then you have a totally different issue.
 
this thread is about opening a project from a while ago that will now not open.
may I suggest you open a new thread as your situation really doesn't pertain to this subject.