Make sure the contacts are clean, but I guess your MC has one or more of these faults:
-wrong size of partition (for example it is labeled as a 64MB-MC and a 32MB-Chip is inside).
-bad contact to the SLOT
or as spud42 said: it is simply tooooo slow.
I'm not sure if it really is so slow that this opperation doesn't work!?
Edit: 4Threads merged. ...are you serious?
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