ERRORS

     There are a number of conditions that can generate Toolkit errors,
     e.g. you try to restore a screen that hasn't been saved, the maximum
     number of saved screens has been exceeded etc. Whenever an error
     occurs, the global byte variable W_Error is updated with the error
     number (listed below).

     The Toolkit can treat errors in one of two ways. If the global boolean
     variable W_Fatal is set to true (default) then any error will be
     fatal, i.e. an error message is displayed and the program halts. If
     W_Fatal is set to false then the W_error variable is set but the
     program continues (as best it can!) - be sure to check W_error after
     every window call if W_Fatal is false. It is recommended that the
     W_fatal flag be set to true until your programs are fully tested and
     debugged.

     The list of error codes for W_error are:

     0    NO ERROR
     1    MAX SCREENS EXCEEDED
     2    MAX WINDOWS EXCEEDED
     3    INSUFFICIENT MEMORY TO CREATE SCREEN
     4    SCREEN NOT SAVED, CANNOT ACTIVATE
     5    SCREEN HAS NOT BEEN CREATED, CANNOT ACTIVATE
     6    SCREEN HAS NOT BEEN CREATED, CANNOT DISPOSE
     7    SCREEN HAS NOT BEEN CREATED, CANNOT RESTORE
     8    SCREEN DOES NOT EXIST CANNOT CLEAR
     9    INSUFFICIENT MEMORY FOR SCREEN COPY/MOVE
     10   VISIBLE SCREEN MUST BE ACTIVE FOR WINDOW OPERATIONS
     11   VISIBLE SCREEN MUST BE ACTIVE FOR MESSAGE OPERATIONS
     12   NOT EGA/VGA CANNOT SET CONDENSED MODE

Note: If the Toolkit fails with W_error 3, there is insufficient
      memory available to store the screen. There are two probable causes:

     -    There really isn't enough memory! Try compiling the program to
          disk and executing the EXE file, or check if there are any large
          memory resident programs. In your program, check the available
          memory with the Turbo function MaxAvail.

     -    The maximum heap available to the program has been set with the
          compiler options or the $M compiler directive. Try increasing the
          Max heap by 5000 bytes. The most common reasons for restricting a
          programs heap size is if the program is going to be memory
          resident or if it will call "child" programs with EXEC. In such
          cases, carefully adjust the max heap setting with the $M
          directive to optimize the amount of heap space needed.