I was also having the same problem above when I was trying to convert the file to Altium. I had got this error message
Allegro design file '8MMINILPD4-EVK-DESIGNFILES\SOM Board\LAY-31399_C\LAY-31399_C.brd' not recognized, or version is too old.
Even the Allegro crashed when I was trying to explore all the traces and planes. I needed this correct 8MMINILPD4-EVK-DESIGNFILES Allegro layout file for my company project. Kindly advice and thanks.
Please take a try to open file '8MMINILPD4-EVK-DESIGNFILES\SOM Board\LAY-31399_C\LAY-31399_C.brd' with Allegro 17.2 Version.