Could not open the editor - Problem with Opening any Xpage or Custom Control and How to Fix it.

Yesterday, I discovered a bizarre problem that I thought I would share.   I was working on a custom control when the Domino Designer began acting up.   I closed Designer and Notes and restarted.   After doing so, I could not open any xpage or custom control and got the following message when I did.

The 'Details>>' button showed the stack trace, with the exception being "org.xml.sax.SAXParseException: Premature end of file."

At first I thought it was my 9.0 client, then I thought it was our development server.   It turned out that it was a corrupted design element causing the issue.   I found a tip online to try using the Java perspective, and sure enough there was two custom controls with the same name.   The funny thing was that I hadn't touched that particular control for several days.   It turns out, that the message was actually telling me the problem control all along.   I chose to delete both copies of the control, and I was then able to continue working.

Here is what the controls looked like in the Java perspective.  I don't know why there is a UNID next to the name, but none of the others have that.  Perhaps it is because of the duplicate name.   The fourth one is likely the problem, but I deleted them all since I didn't need them.  I suspect that if the corrupted control was one that I needed then I would be out of luck.