Sorry for reply the letter so later,because I found the mail in the box now.
When SQLEXEC return 0 ,it happens at the "Asynchronous" mode of the connection
to SQL server. You must resend the command to the SQL.

do while .t.
ans=SQLEXEC(...)
do case
case ans<0
return "error to connect to SQL"
case ans=0
** loop for re-do the SQLEXEC(...)
otherwise
return "I got the anser from SQL"
endcase
enddo

If the connection is by synchronous mode,then the SQLserver will over the sqlexec and send the result to you,so it's better and faster to use synchronous mode in your program.