Make sure you are using Ram Concept 5.0.2. Older 5.0.0 and 5.0.1 commonly had issues importing AutoCAD files.Also, make sure the CAD file is NOT OPEN when tying to import it into Concept.
Problem Internal error importing dwg fileAn Internal Error had occurred.Object reference not set to an instance of an object. (Or similar)Happens importing certain kinds of DXF/DWG polylines, unset text fonts, etc.
Solution Workaround: Fixed for v5.0.2.If you cannot use v5.0.2, then, the same drawings can be imported into v4.1, and then the contents of the drawing import layers can be copied and them pasted into the v5 file (both versions can be installed on the same PC). Saving the drawing as a R12 dxf file and then importing the dxf file might also work. You might try saving the CAD file to an earlier release format (or even a dxf format) and/or purging it of any unnecessary data (delete 3D elements and references, explode and purge the drawing).