Omniplan pro 3.14 (mac) not export to .mpp

When attempting to export to .mpp or .xml I get an error message:

Error Domain=com.omnigroup.OmniPlan.ErrorDomain Code=0 “There was an error exporting this file to Microsoft Project XML Data Interchange.” UserInfo={NSLocalizedDescription=There was an error exporting this file to Microsoft Project XML Data Interchange.}