Thanks for this hint.
On our systems all temp files are located on ramdisk X:.
After extending access rights similar to C:\Users\web\AppData\Local\Temp (= %LOCALAPPDATA%\Temp), everything works like expected.
Extending the access rights to full access had been done by:
With PDFcreate!6.x it was working with read/write/list/change access rights only.
Now full access for PDFcreate!7.0.323 seems to be needed, read/write/list/change isn't enough!?