As a general comment, I'll second what Adrian Welsh stated in regards to the many advances ESRI has made in recent versions in regards to CAD - GIS conversion; many strides have been made and it is much easier now. It used to be real "hit or miss" as to whether things could come across and one would often have to employ several methods to transfer all the information, then add it together and clean it all up.
As to your specific issue, I don't know if this is the cause, but I will mention it as it can be a common issue (it is something I run into alot). What may be going on is the 3D format is causing the issue. The CAD file likely contains Z values, but the GIS format you are trying to export it to doesn't handle them. What one can do to solve this is to use the Environments settings to disable to Z values when importing the CAD data. The following help article, though it is for a slightly different issue, covers the process:
How To: Remove Z- and/or M-values from a feature class
If by chance the issue is on the CAD side, here's a post with a similar issue on the Autodesk Forums that may provide some insight:
MAPEXPORT Xref - Autodesk Community
Note that XREFS are often a major culprit when transferring AutoCAD data to GIS. If you have access to AutoCAD, it can be helpful to embed the XREFS before trying to do the transfer to GIS.
Also, I'll throw out a software package that I've used in the past and found to be very helpful with CAD to GIS conversion. You can download a Trial Version and see if it helps.
DWG to SHP| DXF to SHP|The Easiest, Fastest SHP Converter - Free trial Download - CAD2Shape 7.0 - gu...
Chris Donohue, GISP
As mentioned to Adrian, I unfortunately cannot post any of the files I am having problems with here, I wish I could.
