anybody have any idea?

I got that problem too.
The first 600MB got backuped as expected, but then every single mail produced this error (errno 13, permission denied)

+1

after trying to backup label the permission denied points out to this file
labels.txt.bak

help

Versions 106 & 107 does not store backed-up messages in subfolders (as of v106), don't know if it's a bug or change

and when the number of messages reaches 8,888 the backup process begins to show

IOError:[Errno 13] Permission denied

and messages are not backup up; if you move some backed-up messages to another folder, it restarts backing-up again until it reaches 8,888 files and failure messages shows up.