Actually - Think I may have a solution to the above, obtained via the pro tools forum..
If you get the crashing of either modo drums, bass or Lurrsen, then you can do the following to hopefully rectify it (worked for me):
1. Save your preset on the offending plugin if possible.
2. Save the session.
3. Remove the offending plugin from the insert part of your track(s)
4. Save the session
5. Re-insert the offending plugin to the required track(s).
6. Save the session
That fixed it for me - the forum said it seemed to be a corruption in the session data so doing the above cleared out the corruption..
Happy days, I can now use modo drums, modo bass, Lurrsen in my protools sessions without issues..