I have been running a few tests and something really weird happened in the process.
First I installed AutoCAD 2005 and besides a few compatibility errors I was able to execute it; and when I tried to open one of the dxf samples generated by the library, I got the error you were having. But, after a few attempts to fix the problem AutoCAD
stopped working with a hard crash, after that I was not able to execute AutoCAD again.
Then tried AutoCAD 2006 everything went ok and didn’t have any problems loading the dxf samples. Also I tried out AutoCAD 2004 LT without problems.
But the weird thing happen when I reinstalled AutoCAD 2005, to my surprise when I loaded one of dxf sample it did it correctly with no errors.
So, if I cannot reproduce the error again it is going to be hard to find out what is going on. Maybe some shared library got upgraded in the process, I don’t know. The only advice I can give you at the moment is to upgrade your AutoCAD and see what happens.