Use these steps to see if any subprojects exist in your MSP file prior to importing your MSP project into PM Compass.
For more information, see MS Project Professional External Subprojects.
To use the Subproject File field:
In Microsoft Project, add the Subproject Files column to the view.
Click on the header to display the column options.
In the Filter section of the menu, confirm that (Select All) and (Blank) are selected and that everything else is cleared.