This only applies if you are running the Scheduler as a Windows service.
If you have Excel sources in your Workflow, and the Reader/Writer type for the file block is Excel rather than different Omniscope Reader, then you may encounter the following problem (found in the Scheduler log):
An error has occurred attempting to save the Microsoft office file. Please ensure your Office licence is still valid and that you can save files in the Office application.
Microsoft Office error: Error communicating with Application
Possible solution, suggested on the msdn forum, is to create the following folders:
If the above workaround does not work, then change the reader type to "Omniscope".