A20 line already enabled, so test is meaningless
DPMIINST generates this message while you are running it to locate and add information about your machine to the kernel's database. If you encounter a series of these messages, it probably means that HIMEM.SYS is loaded.
Remove HIMEM.SYS and boot with a plain generic CONFIG.SYS and AUTOEXEC.BAT. Then, run DPMIINST again before reloading HIMEM.SYS.