Seriously, you can't open 3.1 files on 3.0!? That's outrageous.

Jasmine Miller wrote: My university used 3.0 and at home I have 3.1. Not allowing 3.1 files to be opened on 3.0 seems like a money grubbing thing. I find it hard to believe that the programs are so different that they are completely incompatible. PTC seems to be just trying to force people to pay them more money.

I would imagine that your University is on a PTC maintenance contract for Mathcad.  If it is, then it's a Univeristy choice to upgrade or not.   Often organizations don't because they don't want to spend the money paying for their IT provider to do the upgrade, or they have concerns about compatibility, or they have concerns about training staff on the updated software and/or revised coursework, or ...  (I know one major organization that is still running Windows XP and Mathcad 14 over such concerns - nothing to do with PTC).

As for why PTC chose not to make Prime 3.1 compatible with earlier versions of Prime ... that's another matter; it may be that the changes from 3.0 to 3.1 meant that the old format was inadequate for the task and the necessary file format changes were too difficult to ensure compatibility.  Of course, they could have seen this coming and tried to adopt a policy of "If I don't understand it, I'll pring an error message and skip it" throughout the various versions.  Or they could have provided a "Save As 3.0" facility (like Real Mathcad does for its earlier versions).

Stuart