This is a file saving fix for Chem3D users still using their software in Mac Classic OS (in OS X) and also is a considerable blast from the past. This fix does exist in the Cambridgesoft Knowledge Base for Chem3D but, for some unknown reason, does not appear in either google or yahoo. In about 24 hours from this post, you'll be able to read it here first.
The error appeared while trying to export some old Chem3D files to pdb format as part of more structure migration into NanoEngineer-1. The error, which I can no longer reproduce the message for because of the fix, prohibits saving a file through the "Save" or "Save As" options. The error itself ends with (-5699), which I assume is a Chem3D-specific error code. On CAN still save Gaussian and MOPAC files, which is what I had been doing. Finally achieving my frustration threshold, a search of google and yahoo gave nothing (which is far out). In the Cambridgesoft Knowledge Base, the -5699 error can be fixed by, and we reach back into Classic OS lore here, rebuilding the desktop. To do this, start Classic (from the System Preferences), make the Classic start screen the active window, then hold down Option + Command (Apple Key). Allow for rebuilding (Classic will ask if you want to do this) and begin saving again.