Periodic crashes, MC freezes: AppHangB1 / iLok issue?

Errors, lacks
- After 1st install I got the iLOK license manger error, just like here:
http://avid.force.com/pkb/articles/en_US/Troubleshooting/iLOK-license-manger-error-with-Media-Composer

- I then installed the most recent version of the iLok license manger

- Opening a 1-minute-sequence sometimes takes 3" to 5"

- periodic random crashes while rendering a sequence or when trimming or whenever

- 1st: MC starts to get slow. 2nd: little white flash. 3rd: komplete freeze. 4th: after a mouseclick I get a white, transparent overlay on both displays with the following Windows error message:
"Avid Editor is not responding" (problem details at the bottom of this post)

- over all performance is bad

- single frame movements with pressed shift key are sloppy

- PrPro, PS, AE, AI, C4D didn't cause any crashes - so far.
But I didn't do particular testing.

- I encoded a lot with AME with no failures at all.



System

- MC 8.9.3 Symphony Opt, w/ dongle

- Win 7pro 64, fresh install (all essential updates installed via Windows Update)

- BIOS J61 v3.91

- nVidia P2000 (driver, according to Avid's version matrix: R384 U1 (385.08) WHQL /custom installation >clean install)

- Workstation, BIOS and nVidia configured accordingly to Avid's config guideline
"Windows Classic Theme" (which seems to be a thing regarding 3rd party audio plug-ins)
AJA driver v13 installed (but I did most of the tests w/o the io Express attached)


What I tried
- CPU stress test (Intel Extreme Tuining Utility): passed

- RAM: Windows Memory Diagnostics utility: passed

- complete (!) uninstall and re-install of MC + NVIDIA driver


Suspect iLok
- After first installing the mot recent iLok version I then installed the legacay iLok version and the system seemed to be much mor responsive.


TIA and sorry for the longwinding post!

TIA


Description:
  A problem caused this program to stop interacting with Windows.

Problem signature:
  Problem Event Name:    AppHangB1
  Application Name:    AvidMediaComposer.exe
  Application Version:    8.9.3.47085
  Application Timestamp:    59f000e8
  Hang Signature:    87e3
  Hang Type:    0
  OS Version:    6.1.7601.2.1.0.256.48
  Locale ID:    1031
  Additional Hang Signature 1:    87e39fd8069b265b4a993a30d0cde3ff
  Additional Hang Signature 2:    590a
  Additional Hang Signature 3:    590a1065bcbde3bf30fbf4fba49719fd
  Additional Hang Signature 4:    87e3
  Additional Hang Signature 5:    87e39fd8069b265b4a993a30d0cde3ff
  Additional Hang Signature 6:    590a
  Additional Hang Signature 7:    590a1065bcbde3bf30fbf4fba49719fd