Full debug turned on gives you no more info?
So originally the site was a 3.1.1 and you upgraded via steps to 4.1.highest.
What you have now ... a 4.3.highest. Is that right?
What steps did you take the site through in the 'march'?
http://www.syndrega.ch/blog/#php-and-dbms-compatibility-of-major-moodle-releases
I take it you did not stop at each hop upwards, check the site, then make a site backup?
Now we have a fresh 4.3 and attempting to restore course backups - which are of what type?
Full user or just course shells ... no one assigned ... mbz files have nu in the filenames?
Do you have command line access to your server?
Sorry if response isn't providing any solution, but I really can't tell where you are and what you've done ... nor what you are trying now!!!!
Even though you might now want to, am leaning to agree with Emma! Start over ... yes, you up against crunch time ... put on some coffee! :|
'SoS', Ken