User Control Not Set To Instance

I've created a user control (an "extended" rich text box: extended with standard editing). I used the same procedure I used to previously create a different user control (which works just fine)

That is, I:
- Create a Class Library project
- Then Add New Item> User Control
- Then delete the initial class that was added automatically (usually named Class1.vb)
- Put all of my code and components into the user control class.

It was running (with start degugging in the IDE), but I must have done something different since I now get an error:
"Failed to create user control ExtendedRTFBox.ExtendedRTFBox
The error message was 'Object reference not set to an instance of an object'

I tried explicitly creating a public new in the 'ExtendedRTFBox' user conrol. I tried adding a class and adding a dim textBox as New ExtendedRTFBox. I cannot add a starup object in the project properties application tab.