Pro Tools Crashes when opening or closing sessions

Hi everyone,

PT launches fine. I can open a session and work. The moment I close the session or save a copy PT crashes.
Sometimes PT crashes upon opening a session.
Once a session is running, it seems stable. I just can't switch sessions. Has anyone come across the same issue?

System configuration:
MacBookPro 15"mid 2014, 2.8GHz i7, 16GB ram, 512GB SD drive
OSX 10.11.1, ProTools 12.4HD (the same happened with 12.3.1)

What I've tried so far:

• reboot
• trash PT prefs
• reboot + clear PR ram
• moved all plugins to 'unused'
• re-installed Pro Tools
• updated HD driver
• removed old interface drivers (found some Mbox2, RME, UAD, motu stuff that I'm not using anymore)
• ran the Terminal sudo/.... command line that repairs disk-permissions
• created new user account, logged in as new user - still crashes
• ran session from external HD - still crashes

FileVault is disabled.

Mmmm. In older PT versions I'd now trash the digidesign databases, but they don't exist anymore...

What am I not seeing here, what am I over-looking?

The crashes started after installing the ElCapitan recovery update, hence my suspicion it may be HD related - however this may be completely unrelated. At the same time I installed a bunch of PSP plugins. But removing those didn't fix it...

Thanks for any tips and hints!

Pro Tools Crashes when opening or closing sessions