Sometimes it happens to me that either DOPE or the button in the right top corner (On-page editing is the title) stops working. I restart the site, commit the code and test this on test server, but it still doesn't work. Than somehow it gets fixed, but it's really annoying and I don't understand what causes that.
I am mostly using chrome, but same thing happens in FF and IE. This is the FF console screenshot. http://img94.imageshack.us/img94/5215/errorzrp.jpg
Thanks in advance!
Figured it out!
I have renamed a property of backing type PropertyAppSettings and of course, renamed AppSettings key, so the key for the previous property (which was still in the DB, with Missing flag in From code field - displayed in Admin mode for the block type).
I think this has to be fixed by EPi, as it is something that happens all the time. When this happens, the block/page is unusable.