Anton,
Almost all file dialogs are OS specific, so it may be next to impossible to determine the cause of this error.
Regarding 6.04, I have it installed C6 (trial) on a fresh and fully updated Vista 32 bit system without issue other than the odd audio glitch which happens on each subsequent version as the algorithms modified to accommodate changes in the OS.
Maybe you could try installing the 32 bit version to see if there is a problem in the address space of your computer (32 bits will run in a single 4GB address space, maybe this is where the problem lies).