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       EVERYTHING YOU NEVER WANTED TO KNOW ABOUT TOS ERROR NUMBERS
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The GEM function which displays "TOS Error #..." does not display in
the alert box the actual error value returned by GEMDOS or BIOS. 
Those return values are negative numbers (e.g. GEMDOS error -66 is
"Invalid program load format").  Negative GEMDOS error returns are
translated to MS-DOS error numbers for the form_error() alert box you
see.  BIOS errors result in a "Critical Error" alert, which gives you a
chance to retry the disk access that caused the error.

For those of you with a furniture fetish, here's a table:

                           GEMDOS  MS-DOS
 Error description         error   error    Alert text (TOS 1.4 and later)
 ------------------------- ------  ------   ------------------------------
 Invalid function #         -32      1      TOS Error #1.

 File not found             -33      2      This application cannot
 Path not found             -34      3      find the folder or file
 No more files              -49     18      you just tried to access.

 Too many open files        -35      4      This application does not
                                            have room to open another
                                            document.  To make room,
                                            close any document that
                                            you do not need.

 Access denied              -36      5      An item with this name
                                            already exists in the
                                            directory, or this item
                                            is set to Read Only status.

 Invalid handle             -37      6      TOS Error #6.

 Insufficient memory        -39      8      There is not enough memory
 Invalid memory block addr. -40      9      in your computer for the
                                            application you just tried
                                            to run.

 Invalid drive              -46     15      The drive you specified
                                            does not exist.

 Not same drive (on rename) -48     17      TOS Error #17.

 Seek out of range          -64     n/a     TOS Error #33.
 Internal error             -65     n/a     TOS Error #34.
 Invalid prg load format    -66     n/a     (the infamous) TOS Error #35.
 Setblock failed            -67     n/a     TOS Error #36.

Note that some MS-DOS error codes do not have equivalent GEMDOS errors,
and some GEMDOS error codes do not exist in MS-DOS.

TOS Error #35, probably the most common error alert that is not self
explanatory, happens when a program you are trying to run has somehow
been corrupted.  What it means is that TOS can not find some magic
numbers it expects to find either at the beginning or at the end of the
program file.  This error is usually attributable to operator error (as
in trying to execute an archive or text file as a program), or to bit rot.


Here are the BIOS "Critical" errors, and the alert text you see when
they happen:

 Error description          TOS error   Alert text (TOS 1.4 and later)
 -------------------------- ---------   ------------------------------
 Basic, fundamental error       -1      Your output device is not
 No paper                       -9      receiving data.
 Unknown device                 -15

 Drive not ready                -2      Drive X: is not responding
 Unknown command                -3      Please check the disk drive,
 Bad request (invalid length)   -5      or insert a disk.
 Seek error                     -6

 CRC error                      -4      Data on the disk in drive
 Unknown medium                 -7      X: may be damaged.
 Sector not found               -8
 Write fault                    -10
 Read fault                     -11
 General failure                -12
 Bad sectors on format          -16

 Write protect                  -13     The disk in drive X: is
                                        physically write-protected.

 Media change                   -14     The application cannot read
                                        data on the disk in drive X:.

 Insert other disk              -17     Please insert disk X
                                        into drive A:.