This seems to be a common problem now. Maybe it's the whole problem. OK, we can dream anyway.
- Googolians Blog: We're sorry, but we were unable to complete your request.
- RBS: Guess What?
This problem has been commonly associated with blogs that started out as Classic, and were migrated to the Beta template.
We suspect (but can never be sure) that Blogger Support is working on this symptom, which appears to have several possible causes.
One cause is corrupt feeds being added to the layout. When you see the error, go to the Layout Editor, and look at any feeds that you added to the blog. Edit each one. One or more will show "Invalid URL". Delete any feeds with that error.
Another possibility originates with having multiple contributors, and may be caused by multiple contributors changing the layout simultaneously. I'm not sure whether there's an easy solution to this. Blogger Development may have to add template locking.
I've also observed problems caused by moving layout objects, using drag and drop. If an object is easy to create, you may want to extract its code, and add it in another location. Then delete the old object.
We are currently tracking this issue, in RBS Beta: Corrupted Template?. You will find several threads in the Google Blogger Help - Troubleshooting forum.