You fixed it by removing .kde i.e setting it back to defaults…
…Just to check I deleted the .kde4 for my account and I can then log in so definitely something wrong with the .kde4 somewhere…
So do the same…
Clearly you don’t know it was working at the time you took the backup… or lets word it another way how do you know? It’s not like the backup is from a week ago.
… then restored the .kde folder from a backup taken yesterday evening…
Now were this a backup from say a week ago at least it would narrow it down to restore problem at the moment it is just hearsay. A few hours before you noticed the problem is no way to troubleshoot, there is too many variables. i.e had it been rebooted etc… etc…
If it’s permissions it’ll be easy to see just have a look if .kde is owned by root then we’re starting with something.
Edit
You’ve done something different then, if you maintain you tested it… Otherwise why wouldn’t it work now?
At the moment we have contradictions
I know how to restore and it is a working backup
with
I can’t restore with the backup…