Hmmm. I've never had any problems, but here's what I've done with user controls:

I drag the control from the project view tab onto the aspx designer, and then I've not had a problem. I am not familiar with the user control tab that you speak of.

Also- the message sounds like maybe VS.NET wants you to build your solution in order for the control to be available.

Hope that helps a bit- I'll look for your next posting.

db