I got this error when upgrading from 1.3 to 2.0.
warning: array_merge() [function.array-merge]: Argument #2 is not an array in /.../update.php on line 173.
warning: Invalid argument supplied for foreach() in /.../update.php on line 337.
Is there a special upgrade path to 2.0? Normally I just take the site offline, remove the old module folder, copy in the new module, and run update. However, when I did that flag 2.0 threw the above error.