When doing backups with Moodle 2 and the new backup and restore I get an error:
"Can not read file, either file does not exist or there are permission problems"
I found that backup.zip is not created. $zippacker->archive_to_pathname() uses ZipArchive->open() with the parameter ZIPARCHIVE::OVERWRITE and as the file backup.zip does not exist the function returns false.
To fix it on my build I added a few lines in backup_stepslib.php before the call to $zippacker->archive_to_pathname() to create an empty file called 'backup.zip'. This seemed to fix the issue.
May not be the most elegant way to do this but it fixed the issue.
This is only an issue on my Windows install of Moodle 2 on my linux install this is not an issue.