Hey, I can't help much, except that I can confirm that I have the same problem.
I see here that the problem was SiteSeeker (although I don't see how, but I do have SiteSeeker installed - do you?).
I don't have any js errors in the console and my permissions are set correctly.
Perhaps this should be reported as bug to EPi?
We don't have siteseeker, and no js errors. We do get IsSuccess: false from the server, but the block is still moved.
Do you know how to report bugs?
As far as I can see, it's here http://world.episerver.com/Support/Register-Support-Incident/. Does anyone know if this is the correct place?
Will you report this or do you want me to?
Sorry for late answer. I have just now reported the issue. I'll update this thread if they give me any new information.
Posted about this problem in July, see thread:
http://world.episerver.com/Modules/Forum/Pages/Thread.aspx?id=73384
It's about a problem moving blocks between folder. I got promted with a message box that tells me about a problem moving the block, but the block itself actually is moved. I use the cut and paste option since drag and drop does not work here.
Our customer is having the same problem and I need to know if this is a bug.