If you are unable to load an exported DXF file into AutoCAD, most likely it is because either the layer name or block name (i.e. job name) in the DXF file exceeds 32 characters.  Another cause can be illegal characters such as "$%#\" in the layer or block name (i.e. job name) of the DXF file.  To fix this problem make sure to limit your layer & job names to 32 characters or less, and eliminate any invalid characters.