I had the same problem initially but I have been able to fix it.  Here is what I did wrong.  I had installed 2008 Volume 3 for CLR 3.5 but the samples are for CLR 2.0.  Once I installed 2008 Volume 3 for CLR 2.0 the problem went away.

This message comes up when our controls are unable to locate the Infragistics.License file in your Global Assembly Cache (GAC).  Take a look at your GAC (in "C:\Windows|assembly" on Windows XP or Vista) to see if you can find this file.

If not, our installer package may be able to recreate it.  Since you're using a trial version, the only way to do this is to uninstall the toolset and reinstall.  If you had a license key, or if you obtain one, you would be able to run the installer and choose the "Upgrade from Trial" option, providing your license key there.

If this doesn't resolve the problem, or if the Infragistics.License file is there anyway, then this will take more research to determine what's happening.  In this case, please submit a support request so that a Developer Support Engineer can help you further.  You'll probably want to include a link to this forum thread, as well as mentioning what you've done already, so that we don't repeat suggestions that you've already tried.