Do a search on "Visio error 3400". You'll get several hits from others
getting the same error, but not in the same situation as you. This often
seems to indicate a problem with the file possibly being corrupted. Does the
problem occur on the initial conversion of the AutoCad file or is this a file
that was previously converted and saved. If it is the later, try reimporting
the AutoCad data to see if you can get a working Visio drawing again.
If this doesn't work, you could try saving as .vdx (Visio's XML format).
Then try opening the .vdx file in Visio. If you are lucky you can get a
drawing without errors, but you may loose some data in the process if the
file is truely corrupted.
