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 Troubleshooting problems with the swap function
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 The most common problem when using the swap function is that the COMSPEC
 environment variable is not pointing to a valid DOS command processor, so
 check that COMSPEC points to the correct COMMAND.COM for the version of DOS
 or Windows that is running.

 If this is not the cause then the next step is to use the functions
 SWPERRMAJ() and SWPERRMIN() to identify the cause of the error. Please refer
 to the online help for more details on using these functions.
 If these functions do not return a meaningful value, or the solution
 indicated for the error code does not apply or does not help, the next step
 is to attempt to swap to a DOS command prompt by specifying COMMAND.COM as
 the child process.

 If even swapping to COMMAND.COM is unsuccessful with the original parent
 program then create a small test program which simply swaps to the child
 program and displays any error codes on return. If still unsuccessful then
 try swapping from the test program to a DOS prompt as described above.

 Please also read the section entitled `Running protected mode programs' in
 Chapter 3 for certain details and restrictions on nesting multiple DOS
 extended programs. A particular example of this is when running a DOS
 extended program in a DOS box of Windows and then swapping to PKZIP, which
 is also DOS extended. The PKZIP command line parameter `-)' must be
 specified in order to disable the use of DPMI by PKZIP.