Updating to 5.4 (from 5.3.3.1) successful but I can't edit now

Permalink
I can't add content to blocks. "Access denied."

I can't Exit Edit Mode. Browser just waits for C5 to do something.

 
deckeda replied on at Permalink Reply
Downgrading back to 5.3.3.1 by dropping in my old /concrete folder seems successful.
downunderdive replied on at Permalink Reply
I have the same problem, surely theres a way to fix it without going back to an outdated version? Anyone got any ideas?