Notice: Undefined offset: 0 in theme_file_upload_help()

I've enabled the FileField Sources Plupload module and the corresponding feature in my file field settings.

When i visit a node editing page, i see this:

Notice: Undefined offset: 0 in theme_file_upload_help() (line 930 of /var/aegir/platforms/drupal-7.15/modules/file/file.field.inc).

When i upload a bunch of files, i see this:

• Notice: Undefined offset: 0 in theme_file_upload_help() (line 930 of /var/aegir/platforms/drupal-7.15/modules/file/file.field.inc).
• Notice: Undefined offset: 0 in filefield_sources_plupload_element_value() (line 142 of /var/aegir/platforms/drupal-7.15/sites/all/modules/filefield_sources_plupload/filefield_sources_plupload.module).
• Notice: Undefined offset: 0 in filefield_sources_plupload_element_value() (line 142 of /var/aegir/platforms/drupal-7.15/sites/all/modules/filefield_sources_plupload/filefield_sources_plupload.module).
• Warning: Missing argument 2 for file_validate_extensions() in file_validate_extensions() (line 1678 of /var/aegir/platforms/drupal-7.15/includes/file.inc).
• Notice: Undefined variable: extensions in file_validate_extensions() (line 1681 of /var/aegir/platforms/drupal-7.15/includes/file.inc).
• Notice: Undefined variable: extensions in file_validate_extensions() (line 1683 of /var/aegir/platforms/drupal-7.15/includes/file.inc).
• Only files with the following extensions are allowed: .
• Warning: Missing argument 2 for file_validate_extensions() in file_validate_extensions() (line 1678 of /var/aegir/platforms/drupal-7.15/includes/file.inc).
• Notice: Undefined variable: extensions in file_validate_extensions() (line 1681 of /var/aegir/platforms/drupal-7.15/includes/file.inc).
• Notice: Undefined variable: extensions in file_validate_extensions() (line 1683 of /var/aegir/platforms/drupal-7.15/includes/file.inc).

No files are uploaded. Thus, the module is unusable.

Status report is green:

Plupload library: 1.5.4

Help!