We have inherited from the UltraTabControl to create our own tab-control which supports design-time editing, etc. On our development machines (which have Infragistics' NetAdvantage for .NET 2009 Vol. 1 installed), everything works fine.  The controls can be created and used perfectly.  But on our testing machines (which install our application rather than run it through the IDE), the attached LicenseException is generated whenever one of these controls is made.  Our installer process installs the Infragistics DLL's into the GAC, and works for every other IG control except the tab control.  We are not mixing versions, though we do have separate projects in the solution which use the Infragistics' WPF libraries (can't imagine how that would affect this, though).  Every Infragistics DLL referenced in our solution is the same version- 2009, Volume 1 (9.1).  At this point, we are at a dead-end and I am hoping you can provide some assistance.  What could be causing this problem?  Why is the tab control the only control with this problem?