What brand of DVDs did you use? Some PS2s (Especially those with older laser systems, or PS2s with worn lasers) can't read cheap DVD discs.
Originally Posted by TheNM22
You should use high quality DVD-R discs (Verbatim DVD-R discs with AZO) to reduce laser wear and to prevent such problems from occurring.
And if your disc can be burned up to 16x speed, you should burn them at around 8x-16x (If the speed is too low, the quality of the burn may be affected).
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