Hi Tim Solid Edge ST6 support opening AutoCAD files Version 12- Current. Current means the version of AutoCAD available at the time Solid Edge ST6 was delivered. In this case AutoCAD 2013. However the format of AutoCAD did not change in 2014, so you should not have a problem opening file saved in this version either.
If you would like, I can take a look at your AutoCAD file if you care to send it to Steve.Weatherwax@siemens.com?