1202: DOS read error in file <filename> 
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  This message indicates that DOS returned an error while reading an
  overlay file.

  A number of situations can cause this error to occur frequently and
  consistently:

  (1)  The most common is the use of a 'file handles' routine within the
       program to increase the maximum number of file handles available to the
       program under DOS versions 3.0 to 3.2.  If this 'file handle' routine is
       called after Blinker has opened the overlay file and loaded one or more
       overlays from the file, the file handle table is recreated, wiping out
       Blinker's existing file handle for the overlays.  To avoid this, ensure
       that the handles function is called from the root before Blinker has
       loaded any overlays.

       A combination of three factors can cause this to occur in a Clipper
       application: (a) Calling one of these handle table expanding
       routines such as FUNCKY's SETHANDLES() or NETLIB's NHANDLES() from
       an overlay, (b) Using versions of DOS 3.3 or above, and (c)
       specifying the CLIPPER Fn environment parameter. Since the
       handle-increasing routine is only needed for DOS versions 3.0 to
       3.2, this error can be avoided by checking the DOS version before
       calling that routine:

          IF DOSVERSION () < 3.3
                SETHANDLES (29)
          ENDIF

  (2)  This error can also occur when non-overlayable modules are
       placed in the overlay area.  If there are any .OBJ or .LIB files
       in the overlay area which are not known to be overlayable, then
       these should be moved to the root and the program relinked.

       If the program then runs successfully, this indicates that the
       file(s) are not currently overlayable (see the file 3RDPARTY on
       the distribution diskette for an up-to-date list of libraries
       which are known to be overlayable; or call our Technical Support
       BBS to download the latest version of 3RDPARTY.

  (3)  Should the program stack overflow, it can overwrite the
       nearby file handle area, resulting in this error.  Try increasing
       the size of the stack with either the STACK or BLINKER PROCEDURE
       DEPTH command.

  (4)  A network could be configured to deny access to the .EXE once
       it had been loaded, preventing Blinker's overlay manager from
       reading an internal overlay.  Also swap functions can result in
       this error if the file handle table has not been restored
       correctly.

       Finally, if this error occurs sporadically, it is a more
       difficult situation to diagnose.  Possibly the overlay file has
       been closed by an external influence such as a TSR or being
       logged off a network, or the overlay file has become corrupt
       because of a disk error and should be reinstalled.