Another "file could not be loaded into the designer" issue

[Chris Snyder]

OK. Here's the short form:

I have a non-abstract base page class that other forms inherit from. I
keep getting the infamous "file could not be loaded into the designer,
file name <x> could not be found.

I tried checking the context in the OnLoad, no luck. None of the
solutions in the help file apply to me. However, I have found that if
I change the return type of one property, everything works fine.

Before:

protected IUBE.UserSet UserSet
{
get { return this.Session[IUU.SessionConstants.UserSet]; }
}

After:

protected DataSet UserSet
{
get { return this.Session[IUU.SessionConstants.UserSet]; }
}

While on the surface this does not seem like a big deal, it requires
all my inherited forms to cast the return from the property. Quite a
bit of work, just for design mode functionality.

Anyway, it seems to me that the Designer is attempting to load the
assembly containing the definition of IUBE.UserSet, and is failing. Is
there a way to get it to NOT try this, or a way to get it to find the
assembly?

Thanks a lot,
Chris