Problem when using admin.php with nGen File Field

If I use admin.php instead of /system/index.php to access my CP, I get a bunch of errors like

Warning: mkdir() [function.mkdir]: No such file or directory in /home/XXXXXX/public_html/cms/extensions/fieldtypes/ngen_file_field/ft.ngen_file_field.php on line 714

Warning: chmod() [function.chmod]: No such file or directory in /home/XXXXXX/public_html/cms/extensions/fieldtypes/ngen_file_field/ft.ngen_file_field.php on line 715

when accessing publish/edit pages with fields that use nGen File Field but only when logged in as a super admin - not any other member group. But for any member group, trying to upload images gives Something happened while uploading xxxx.jpg Please try again.

If I log in at /system/index.php, all works as it should. Is there something else that needs to be configured when using admin.php or should this be moved to the Extensions forum for feedback from the nGen guys?

[Mod Edit: Moved to the Extensions: Discussion and Questions forum]