Microsoft Project Plan weirdness


#1

MPP files saved from MS Project 2016 and MS Project Web Client fail to import into Omniplan Pro 3.13.1.
But if I save them from Project in XML format, they do import.

Further, if I first open the MPP files in Project Viewer 365, and then save them as MPP files, they do import.
But if I open them in Project Viewer 365 and save them as XML files, then they do NOT open in Omniplan.

As my clients only want to share MPP files (not XML) do I have to purchase Project Viewer 365 as an intermediary MPP file processor, or is there something I can configure in Omniplan to make it happy to open MPP files?