If you run from command line you'll see traces and exceptions in the console. It should give enough details to troubleshoot. Otherwise MS Project XML is a simple format so if you're able to isolate the problem, you can find the cause by comparing a normal MS Project file with the one created by Planning Pro.
I don't see the file attached. If you can add it or send it to lchretienneau@projectlibre.org I'll have a look too.
Thanks.