Thank you for your post.
If it works under one user but not another on the same machine, the only difference is the preferences file. Remove the preferences for the user where it isn't working. The file can be found:
Home -> Library -> Preferences -> com.filemaker.filemakerpro.plist
The next time FileMaker Pro is launched, it will look for the preferences file. When it sees one isn't there, a new one will be created.
it is not preferences. actually it is happening on both accounts.
the error occurs only then pressing return in the Set Variable Options window.
it guess I was clicking Set Field on the other computer when testing.
this is a bug and have posted in the bug area.
so far i have found and reported 4 bugs (fairly obvious ones). since version FMP 2.0 I have never found bugs in a official release of Filemaker before.
not enough testing was done before 10.0v1 was released.