User control gone from toolbox

Hello!

In my program I have a number of user controls, inherited from System.Windows.Forms.UserControl. As soon as a new user control is created it appears automatically in the toolbox. But now all my old user controls are gone from the toolbox. If I create a new user control it will appear as usual.

So my question is, why did my user controls disapear and how do I get them back to the toolbox?

I've tried with "Customize toolbox" and managed to display them in the toolbox again, but then they are displayed with a different icon, a yellow wheel instead of the usual grey rectangular thing. Does this have any importance? Or is it the same thing?

/Sara