Hey why not just get the Pro cfw instead? It has popsloader and iso/cso support built in. You can get it here: procfw - X-Generation Aftermarket Firmware for Playstation Portable
Since you're on 6.20, get that version and run the proinstaller then the pro620bootloader and it loads the cfw automatically...
Or try the TN-E Hen (fix?) floating around out there I think the popsloader was a thing he fixed in it.
Anywayz I didn't have any problems getting the PSX2PSP games running on Pro. You aren't trying to run the original PSX iso, are you? If so that would be a major hassle ... just look up some PSX 2 PSP iso's.... (isozone is good if you can't find it on torrents)