Updates:
 
Chose a project with loads of soft synths & Fx plugins
Inserted TTS-1, crashed as expected. No surprise there
Re-opened the project, removed all T-Racks plugs, insert TTS-1, crash
Re-opened the project, froze all synths, bypassed all Fx, loads TTS - it works!!
Unfroze all synths, re-enable all Fx & it still works
 
All the above "inserts" refer to inserting the synth itself, not the template

Thanks Bjorn, I've got another test routine to perform later on, see if i can narrow this down a bit

This sounds like in some way Sonar is getting mixed up between Rapture and TTS - I had something like this a few years back but unfortunately cant remember exactly all the details. However I'm pretty sure I deleted one or perhaps both the offending plug ins / synths - then went through the registry and got rid of all the entries  - I got the latest versions, then reinstalled them, making sure I installed one of them in a different directory (then pointed Sonar's VST scan to that directory) and I'm pretty sure that did the trick.
Hope this is of some help
Nigel
 
 

I've had weird problems with plugins like a TL64 not working at times. It was showing as a DX and VST plugin. They both had the same path and GUID so what I did was exluded the DX version and all was OK again. No more weird behaviour.

Open the plugin manager and check the GUIDs for each plugin. Select in the centre column and write down the GUID for one and compare it wupith the other.
It could be that they have the same GUID which is causing problems.

Each version of Sonar has its own plugin hive within the registry so there could be a mix up between TTS1 and RapPro.