I was migrating a Windows 7 user from one machine to another when I came across this error. We were upgrading her machine to a 64 bit version of windows. The migration went smoothly, except for this little error. No matter what I did, I could not get it to work. So after getting with the technical chat support, this is what I found and resolved the issue. I figured I would share this because I could not find it anywhere else.
Background Info: The Adobe license were upgrade licenses from CS4.
1. Start Photoshop > Help tab > deactivate
2. Close Photoshop
3. Go to c:Program Files (x86)Common FilesAdobeAdobe PCDCache
4. Rename cache.db to cache.dbold
5. Open Photoshop
6. Enter the upgrade serial for CS5
7. When prompted, enter serial for CS4
8. Open Adobe Acrobat 9.0
9. Enter the serial for Acrobat (The serial for Adobe Acrobat Professional)
10. Skip registration
11. Close Photoshop and Acrobat
12. Open Acrobat, confirm working.
An annoying process, but if this had been in a KB file, it would have been simple.