which is odd as it's one of the approved file types. is it a very big file ? there are file size limits.

Okay loaded the pot into simplify3d - did you by any chance use inches ?
It needs to be in millimetres :-)

Other than that and the lid needing to be the other way up to print properly. The way you've got it it'll need supports.
Looks fine.

Loads fine into makerware desktop as well.
But the pot only 25.2mm tall - and the lid is the wrong way up.