User controls disappear from form.

[Peter Manesis]

I have created some user controls which they inherit from TextBox, ComboBox e.t.c. They seem to work fine but sometimes when I open the project and load the form containing them (or maybe when I change the dll with my controls), then my controls are vanished but actually they are not deleted. When I check the code file (*.cs) I notice that the code has not changed at all, but I can not see my controls on the design form and during runtime. Does anyone know what I have to do?

Thanks in advance.