Hi,
I've been having this same problem as well since upgrading to ArcGIS 10 in September 2011. I'm at a large educational institution, and the export works pretty much everywhere on campus except for the lab where I regularly help architecture students export vectors to CAD. Different areas of campus do have computing IT administered in different ways. Previous to the ArcGIS 10 upgrade, I never had problems exporting to .dwg unless the input files were just too large for it to handle.
I had a breakthrough today, though! It seems that the location of the input or output file has something to do with it. A shapefile in a folder on my desktop was input, output to a .dwg on the desktop, and I had exactly what you describe -- an empty, very small (8k) .dwg file. I moved that same folder to a networked fileserver, and exported it to the same dwg2010 default format, but also to the networked fileserver folder, and it worked perfectly. I'll post as I figure out more about this.
In the past, I tried using the other, older .dwg filetypes, and that made no difference. .dxf has worked fine for us, but the files are typically much bigger in .dxf than they would be if the .dwg was working.
This is the first time I've seen evidence that this is happening to others. I do plan on filing a bug report soon.
Thanks,
Nicole Scholtz
Spatial and Numeric Data Librarian
