>Finally found th e reason for my problem:
>
>The TEMP dir (%TEMP%) had too many files. I deleted files and all is working fine again.
>
>Which leaves as question:
>
>How can I automatically delete unnecessary files without "disturbing" programs that rely on one of that files?
>
>TIA
>Gerhard
>
Simply add try/catch around delete file, so you'll just log file that can not be deleted and proceed with other deletions.

You can also check if the file is used by first trying to get exclusive access to the file.