Uploading file error to this forum.

I've tried to add a message to this forum with a DWG attachment that I created using PDS 2014 Mechanical, but am getting this error:

"The file type doesn't match the type of its contents"

I tried using IE 10 and Firefox 22 but same error.

I have uploaded DWGs from ACAD 2014 before, but this is my first attempt with PDS 2014 Mechanical.

Any ideas how to fix?