Sounds like you do have terminal/ssh access. So do this:
In the Moodle UI get to the screen where you click the button to begin the process and pause.
In terminal/ssh session, login as root and go to the moodledata/temp/backup/ directory.
Remove anything in there first so we can see what we are working with. This is safe to do.
From moodledata/temp/backup/ location: rm -fR * [ENTER] MAKE SURE YOU ARE LOCATED THERE!
Back to the Moodle UI window in the browser - click the button.
Back to the terminal ... do an ls
You'll see a new directory by a long name like 54asdlghqwer;lqwerhi34qwerghsls
cd 54[tab key] which should find the entire long directory name.
Once inside that directory ... this is where moodle builds the backup ... issue the following command:
watch "ls -lR;df"
This runs watch ... which executes both ls -lR in one window and displays how much diskspace is remaining in the second window. It refreshes every 2 seconds by default.
Fairly quickly you will see a 'activities' directory created ... quit the watch command, then reissue it wtih:
watch "ls -lR ./activities/ ;df"
You'll see quiz directories being created by their quiz ID number.
Now IF/when the Moodle UI kicks out the error, the watch window will show where it stopped.
If you note the quizIDnumber directory last created ... you mght be able to then deduce the quiz it was trying to build - and thus, the next time you do this, EXCLUDE just that one quiz.
Yeah, it's involved ... but Moodle UI doesn't provide much help other than a log that shows some numbers ... like 800 ... which, BTW, are tied to what the backup/restore process is currently building, etc.. Think 800 is activities which includes not only quizzes but other potentially heavy data stuff like questionnaires..
The error about the temptable is somewhat misleading, BTW ... there is NO temp table remaining after a failure like this cause the session established with the DB to do the backup process is killed and when MySQL discovers that, the session is ended ... ending sessions auto removes temp tables in MySQL.
Ok ... you offered a look see at the course ... PM me with the URL where I can obtain the backup and I'll load it up on a server to which I have access where I can inspect the backup and try it out there. Is it no user?
'spirit of sharing' ... and going the extra mile! :|