Method System.CodeDom.CodePropertyReferenceExpression.xxx not found.

I have a baseform, which contains an own made component that implements the
IExtenderProvider interface, so that this component provides properties to
the controls in the form.
The IExtedenderprovider is kept in a seperate project (project reference).

Then I try to inherit from this baseform.
When opening the screen at design, (after putting some extra controls on
it), all the controls disappear, and in the task list I get messages like:

Method System.CodeDom.CodePropertyReferenceExpression.SetDataTag not found.

At run time, everything works fine.

What could be the problem with this ?
Is it a VI bug, or am I doing something wrong ?

Thanks !