... what 1074 says. One thing to try, however: I don't go with these folks who recommend formatting the card in the camera every time you use it, but if we accept that there's something odd about Lexar/Kingston cards that the Canon doesn't like, formatting might mitigate it (whatever it is). Can you try copying off all your data and then reformatting in the camera and trying again? Also, can you confirm that you see the buffer icon prior to auto-stop?
I have a Lexar 8Gb Class#10 micro SDHC that works fine.