I’ve just encountered the same issue as Ryan reported in this old thread, but I encountered it in the Wiki.
Basically, my client tried to upload a file that had a .JPG extension in uppercase, but got this error message:
The filetype you are attempting to upload is not allowed
I changed the file extension to lowercase, and it worked fine.
I tried editing /system/lib/mimes.php to add this line: ‘JPG’ => ‘image/jpeg’, but that didn’t help.
Just wondering if you have any other ideas/fixes? I’m using EE 1.6.9 Build 20100805.