Hi Carl,
Please try the following:
1) Make a backup of all files in the following directory:
C:\Documents and Settings\USERNAME\Application Data\Microsoft\Crypto\RSA\S-1-5-21-3747606025-1794718140-643186709-1005
2) After backing up the files, please delete them all.
3) Try running Impression again.
Please let me know if that worked for you.
Nikolai Sander
Sr. Software Engineer, Autodesk