Crash related to non-accessible files?

Dear all,

I have the latest version of Max / MSP installed on a windows 7 computer.
Max works well on one of the sessions of this machine, a non-admin session. However, for two other sessions (another non-admin session and one admin session), it crashes before starting, asking me whether I want to close now or restart (even before I see the max window)

I have tried to
- remove the C:\Users\username\AppData\Roaming\Cycling '74 folder
- uninstall / reinstall
- reboot the machine

But it does not seem to do anything. Once, after deleting the folder and rebooting, I saw the max first start window, but it crashed after a few seconds

Checking my user folder, it seems I have a crash dump in the AppData\Local folder, from which I gather (translated with google translate, as the software is in German):

Dump file: Max.exe.992.dmp: C:\Users\username\AppData\Local\CrashDumps\Max.exe.992.dmp

Process name: Max.exe: C:\Program Files\Cycling '74\Max 7\Max.exe

Process architecture: x64

Exception code: 0xC0000005

Exception information: the thread has attempted to read from or write to a virtual address for which it does not have the appropriate access rights

Heap informations: unavailable

Operating System Version: 6.1.7601

Anybody has any idea why I get this error? And why on some sessions but not on all of them?

Thank you very much!

Laurent