i don't think pmxscan is a standard windows file, therefore my guess is that it came with the scanner.
That being the case, some of the uninstall options don't delete files cleanly.
Try Start->Find->Files to find a file pmxscan*.*, and note where it is.
Then delete your scanner software, and reload your machine.
Repeat the find operations - has the file gone? If it hasn't, try deleting it manually then reinstall your scanner software.