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.
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.