DPMS fails on computers with 512 MB of memory or more
Reason: DPMS (DOS Protected Mode Services) driver was written by Digital Research Inc. for DR DOS 7.0 back in 1991, when average PC had 1-2 MB of memory. It's very likely that 512 MB is hard-coded limit. The source of DPMS driver is currently own by Novell Inc. Therefore we cannot check the above assumption. Unfortunately we are unaware if Novell ever released any update to DPMS driver.
Solution: It appears that only solution is to not load EMM386.EXE in your config.sys. I.e. your config.sys should be similar to following: 
DEVICE = C:\DOS\HIMEM.SYS /Testmem:Off /NUMHANDLES=128
DOS    = HIGH
DEVICE = C:\CARDWARE\DPMS.EXE MEM=XMS
DEVICE = C:\CARDWARE\PCCS.EXE /SC:off
DEVICE = C:\CARDWARE\PCRM.EXE /autodetect
DEVICE = C:\CARDWARE\SSPCIC.EXE <switches>
DEVICE = C:\CARDWARE\PCENABLE.EXE
...