Are you using swapmagic original discs, or copies, or just .elf files?
Are you using ESR with the disc already in the system when you boot? Sometimes this works for me on games that seem to not work if you put the disc in after powering on. Just try putting in the disc with the PS2 off, then turn it on and try ESR again.
DVD+R is fine for your slim, what speed are you burning at?
SCPH-39001 V7 GH-019, fliptop case, FMCB 1.8, 80GB HDD (SMS console) 16MB card running it all
SCPH-39001 V7 GH-022 FMCB 1.8, 120GB HDD (Game console) 64MB card running it all