[xwiki-users] Cannot delete attachment

Hi guys, When deleting attachment, I've got following error message: "Failed to delete attachment: ( The request was rejected by HTTP filter. Contact server administrator. )" It is just a *.doc, added by other user and updated to once to 1.2 version. Tried also to delete as admin to no success. In Sandbox webspace I create, update and delete such an attachment without problems. Search on the web by error message didn't bring correlating results. Can someone hint why is this happening and how to solve it? May it be smth about user rights? Thanks, Andrey Stoliarov