"Insert search engine here" was pretty useless for this one - I've had a look through
wp-admin/includes/file.php etc. but not found a reason for the behaviour I'm getting.
I'm running multisite, and when I upload a .doc or .pdf I don't have a problem. When I upload a .ppt - regardless of the actual filename or mimetype (i.e. a .ppt renamed to .txt, a .txt renamed to .ppt) - I'm told "Sorry,this file type is not permitted for security reasons" with little other explanation.
Do I need to modify the mimes table, add an override (and if so, what's the syntax for this), or is it something in my Apache conf? I've done some funny fiddling to try and lock things down in a few places, possibly blocking .pot files.