With TestAdvantage you always use the version that equates to the version of NetAdvantage that you are using. So in your case since you are using NetAdvantage 2008 Volume 2, you should use TestAdvantage 2008 Volume 2.

    The reason being each version of TestAdvantage is built with references to the corresponding version of NetAdvantage, but those assemblies are not included. When you record or replay with TestAdvantage against NetAdvantage using QuickTest Professional, it uses the already loaded assemblies from your application. If you are app is built using a different version of NetAdvantage then your TestAdvantage then if will throw an exception about missing or duplicate assemblies.

  As to how the version of TestAdvantage relates to QuickTest Professional. All supported versions of TestAdvantage work with all supported versions of QuickTest Professional. It should be stated though that while some of our older versions of TestAdvantage installers, I believe 2007 Volume 3 and back, may have issues installing against a 64bit machine, the assemblies will work against 32bit applications. The installer issue being because 64bit machines changed registry locations, and the limitation of 32bit applications is only because QTP doesn't currently work against 64 bit applications.

First you should verify that the volume of Infragistics TestAutomation/TestAdvantage matches the version of Infragistics/NetAdvantage for Windows Forms since the error you are seeing would happen if they don't match.  If you have verified that and the issue is indeed because QTP is having trouble finding the Windows Forms control assemblies then you may be able to workaround the issue by installing the control assemblies in the GAC with the Global Assembly Cache Tool (Gacutil.exe) or adding them to the bin directory of UFT.