Error message looks like:
Instruction at address access memory at . Memory can't be 'read'

and varies from time to time.

Correction to previous post

Error message looks like:
Instruction at address [some address] access memory at [other address]. Memory can't be 'read'

[some address] and [other address] varies from time to time.

After previous update those messages about instruction at some address disappear.
But other crash variant remains.
Maybe it is specific to Windows 2000.
It looks like: 'Exception unknown program exception (0xe06d7363) in application at address 0x7945bc3f.'
Values are always the same.
In most cases Foldit remains in process list of Task Manager.
Also it happens during Overnight-like script every 2-3 hours on Core 2 Duo 2.1GHz but not on Pentium IV 3GHz. Also it happens when closing Foldit on both Core & Pentium.

Not reported more, client updated. Closing.

Marking as resolved.