User receives error message after selectin/deselctiong subscription

After selecting or deselecting subscription to a newsletter the following error message is displayed ( repetaed 10 times) when a user tries to subscribe or unsubscribe for a particular newsletter category:

Warning: Invalid argument supplied for foreach() i inline_field_attach_validate() (rad 210 av /storage/content/88/176188/rme.nu/public_html/sites/all/modules/inline/inline.module).

It seems the request is handled correctly and the choice is saved but the error message is annoying.
The page is "user/1/edit/simplenews"