a.) in the U310, why no audio in the published work?
b.) why the project file from the 2nd computer cannot be recognizd by the U310?
Welcome to the forum.
When an output file has Video, but no Audio, it is often due to the settings for Multiplexing, in the Publish+Share dialog. Multiplexing combines the Video and Audio Streams into one file. My first act would be to verify that Multiplexing in the Audio Tab in Advanced, is set to something but "None." This article goes into more detail: http://forums.adobe.com/message/3557964#3557964
If that is not the cause, in this case, it would be informative to know exactly which Audio CODEC was chosen for that output. That info gathering could be as easy as just running the file through G-Spot, or MediaInfo, to gather the Audio CODEC in the file.