Maybe I should rephrase this in hopes of getting an answer ;)

When one develops a custom/user control for windows forms, must it be
self-contained in a single DLL (ie, no dependency to other DLLs) in order
for it to be added to the VS.NET Toolbox?

My control for example, is named MyControl.dll, it depends on some common
classes that are from a different DLL (MyCommon.dll) as well as a separate
library that implements a custom license provider (MyProvider.dll). This
means that the output of a build of my control project produces the
following files in the bin directory:
       MyControl.dll    (my user control)
       MyProvider.dll      (custom license provider, shared by several
controls)
       MyCommon.dll     (common classes, shared by many projects)

Obviously the MyControl project *has* a reference to the other two DLLs.
When I try to add it to the Toolbox I get an error indicating that
"MyProvider or one of its dependent assemblies could not be found" which is
strange because all three reside in the same directory! and the control
project *has* a reference to them as well!

Yes, I think that ideally it would be self-contained but in this case -and I
imagine more complex controls also fall in this category- it is neither
practical nor wise to copy all the necessary classes from the other
assemblies into the control project only to satisfy this constraint. It
would be a maintenance nightmare, specially if you deploy several control
assemblies that have the same license provider!

I suppose I am missing some important information, what is it? I really
can't believe that a user control must not reference other "user" assemblies
for it to be deployable in a toolbox. As a result I can't drop my component
into the form. It was possible when all was in one assembly (no common code
usage and no license provider).

Help please =)
Emilio