The WINC1B.EXE patch placed on both CompuServe and the AGV BBS appears to
cause complete failure of the freeplot function in AutoCAD R12/Windows.
You will receive an EREAD error when trying to plot a drawing when using
the -p parameter.  The c1b patch does correct the problems with INSERT ~
and with the F1 help key, and background plotting can still be
accomplished by using one of the 3 sessions available with AutoCAD for
Windows.  However, if the freeplot option is important to your operation,
there is a way to "unpatch" the AutoCAD executable.

At the DOS prompt, type:

    WINC1B /? 

You will see all of the options for the patch.  The parameters

    WINC1B ACAD A 

will take you back to the c1a level of the ACAD.EXE file.