The solution?

You're missing a needed file in Photoshop in the Library/Scripting Additions - the "Adobe Unit Types" file.

If you have another machine running Photoshop CS2, just copy it over from one machine to the other in the same location: under the hard drive, Library, Scripting Additions.

Usually this is a result of an Archive and Install on a machine with Tiger or Panther and CS2 installed.

More info here:

http://www.adobe.com/cfusion/knowledgebase/index.cfm?id=329996

Mike