I am not recommending the MXO2, I was forced into it to use later versions of Premiere. I was perfectly happy with my RTX2, but wanted to move on from PPro CS2. The MXO2 is less fussy about hardware, but lacks all the cheesy Matrox effects - that does not worry me, though.
If you can work with new and other existing projects, then it looks as though your system itself is healthy, and the problem is with this specific project. The downloaded file will not open on my system - I get the error message that you report.