Most older FAT PS2s can't read cheap discs (Memorex is a very good example of a brand that makes low-quality discs) and DVD+R discs.
The odd thing here is that I tried a few of them on a friends fat ps2 and they worked just fine. I have NO idea what's going wrong here since I've done nothing differently than I did before and the games I burned previously work just fine. Any ideas?
Another possibility is that that set of Verbatim discs you've got isn't manufactured by Taiyo... but some cheaper company like CMC.
Stick to only Verbatim (Taiyo) DVD-R discs if your PS2 is one of those PS2s with the older KHS-400 lasers.
A really close situation to what you've experienced: My 39001 PS2 (Before I swapped it for my 39006) couldn't read any of the discs my 39006 can read (Except for those Verbatim discs).
Unmodified SCPH-77006 with SM 3.6
SCPH-39006 with M-chip modchip, SCPH-10281 NA and refurb Seagate 80GB HDD
SCPH-10000 v1.00 with SCPH-10190 PCMCIA NA and SCPH-20400 HDD unit