Possible user profile corruption question

I'm running Vista Ultimate and am encountering a strange problem. On my
normal account, when I copy large files or try to install large appps (that
are not Microsoft products - don't have the issue with e.g. MS-Office- ), my
system seems to be loosing connection to my local harddrives. In a command
prompt box I can see that the error is said to be "account disabled". The
software I try to install then always gives me an "internal error 2502"
message box. All I can do then is reboot the system to gain access to my
disks again. To make sure it wasn't related to the software I tried to
install or to hardware issues, I created a new account on the system. When I
use that account (and as far as I can see it is identical to my normal
account) I NEVER encounter the above mentioned issues.

I am convinced now that there's something wrong with my regular profile but
can't seem to find it. Anyone any idea?

I'm running Windows Vista Ultimate Edition (English) on a system with an
Intel Core2Duo with 2GB memory and 1TB on diskspace (of which 100 free on my
system partition).
The installation was a clean one (So NO upgrade!!!)