1202:   DOS read error in file <filename>

     Note:  This error can occasionally result from the effects of a
     virus.  In this case, first try external overlays (via the SECTION INTO
     xxx command) marking the .EXE read-only, and then follow the procedures
     outlined below.  If nothing else helps, perform an extensive check for
     viruses and take the necessary measures for removal.

     Explanation:  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.

        Note:  A combination of three factors can cause this to occur in
        a CA-Clipper application--Calling any handle table expanding routine
        from an overlay, using versions of DOS 3.3 or above, and 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.

     2. This error can also occur when non-overlayable modules are placed in
        the overlay area.

     3. Should the program stack overflow, it can overwrite the nearby file
        handle area, resulting in this error.

     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.

     5. Finally, if this error occurs sporadically, it is possible that 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.

     Action:  Some suggestions to resolve this error are:

     1. ensure that the handles function is called from the root before
        Blinker has loaded any overlays.

     2. If there are any .OBJ or .LIB files in the overlay area which are not
        known to be overlayable, 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.

     3. Try increasing the size of the stack with either the STACK or BLINKER
        PROCEDURE DEPTH command.

     See also:  The Linker Reference Commands section in the "CA-Clipper
     Real Mode Linker--BLINKER.EXE" chapter of the Programming and Utilities
     Guide.