From the errors you posted it really looks like bad/incompatible card. There is no point in wasting time with it. Get a different card or wait, maybe this will get fixed in next firmware.

Try the card in other devices. Or simply return it if possible and get different one. Looks like n800 simply doesn't like it. In fact I have similar card myself. It it Transcend 4GB MMCplus card. I bought it in advance before getting n800. It was quite cheap but simply doesn't work in N800 and produce similar i/o errors. It does work in other devices - usb reader, Tapwave Zodiac, even in N770 with hacked kernel to accept full sized cards without closing doors, but so far it fails in N800. I hope it is software issue that can be fixed.