Infopath "The file is in use by another application or user."

Interesting error... Confusing... Not at all helpful or accurate. What to do?

1. This issue is not consistant across all users.
   
1. One user with the issue is on XP Pro, sp1
2. Another without the issues is on XP Pro, sp2... need to investigate.

Related threads:

1. microsoft.infopath via google groups - Unresolved
   
2.