Can't upload certain media

My wordpress multisite install is not not letting us upload any Microsoft Office files (.doc etc) even though they are listed as acceptable file types and NOT over the upload limit. - We all keep getting the message - File type does not meet security guidelines. Try another.

I turned off all plugins - and still go the error. HELP! My users need to be able to upload files!
Thanks in advance!

URL - http://blog.burlesonisd.net