Your PS2 does read DVD+DL (if the laser is in good condition, a good DVD-Media is used and the burning-quality is high.).
It is (most probably) a media-quality-issue.
Try Verbatim DVD+R DL, as already mentioned and you should be fine.
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux