When I edit an item in the front end, the delete attachment button does not work. I get the prompt that asks "Are you sure?" but then nothing happens when I click OK. However, the delete button works fine when editing in the back end. Clicking OK at the prompt results in the deletion of the attachment.

In firebug, I get an error in the frontend= "403 You are not authorised to view this resource." related to mootools line 75.

Hi. Please check that you don't have any javascript errors on your page. If you do the request will not be done so your file will not delete. Also make sure that you are using the latest K2 version with the bundled form for frontend editing.

No. This appears to be a problem with the way that core joomla SEO is rewriting the url for the link. I run with the first two options on and the third option off.

The non-SEO link works (with all core joomla SEO options off)
/index.php?option=com_k2&view=item&task=deleteAttachment&id=25&cid=155&Itemid=212&lang=en

The SEO link does not work
/en/organization/ministries/music/item/deleteAttachment/25/155

It appears that the Itemid (in this case Itemid=212) is being dropped in the rewrite. This generates the "403 You are not authorised to view this resource." error in mootools line 75 according to firebug. No other errors.

I am using K2_v2.1_build20090909