No, there isn't anything else that needs to be done... as long as you replaced the references within the Inherited UI DLL to 6.2 and rebuilt it, then it should work for everyone that has 6.2 installed on their computers.  If you registered the DLL in the GAC, then it might be the case that he does not have the exact same version of DevExpress installed on his computer, or he has more than one version (6.1.5 and 6.2, maybe?).

Yep, you were right.  We uninstalled 6.1.5 from his machine and everything magically worked.  The weird part is that I have both versions on my machine but don't have problems.  I figured it's something to do with me building it on my machines that is allowing me to avoid the issue.  Oh well, it's fixed...I should've asked 3 hours ago 

.NET resolved some of the "DLL hell" that you had with the old Win32 stuff, but it introduced a whole new group of problems