Hi, no it's not because they have TFS installed. TFS only matters if you are building the application using TFS and then you need to do some extra steps to register the key. So it isn't that.
When you compile your application it embeds a license for RapidSpell in your EXE, this is part of the standard .NET control licensing scheme. However, the .NET licensing scheme invalidates embedded licenses if your exe is modified, eg.
1. if the file name is changed
2. if a virus modifies it
3. disk corruption
and perhaps other reasons I haven't thought of.
So my conclusion would be that this particular install has been modified somehow.
Probably the easiest first step is to reinstall your software, or at least switch their EXE for your original version. Check that no where is the filename modified after creation, etc.
Hope that helps
Jim
-your feedback is helpful to other users, thank you!