Can't open dwg file in Autodesk 10

[mxpardo]

We have a file created in Autocad that we cannot open. It gets stuck looking for files named yassimp.shx and yascm.shx. I've tried to substitute different shape files and ignore them altogether using the cancel or esc key, but the program crashes before the file will open. I downloaded a trial version of autocad and opened the file and purged it but I get the same result. We've had similar issues before but substituting bigfont or ignoring has always worked. Any thoughts or suggestions would be greatly appreciated. Thanks.