The new 3 Gigabit/second eSATA cards contain a rather large Marvell chip with the string "88SX6081" on it. Previous generation eSATA cards had a Marvell chip labeled "88SX5081". Additionally, you can check your Macintosh System Profile. When you select the installed eSATA card, the Device ID will show either "0x6081" or "0x5081".
This does not happen often, but sometimes the driver caches do not get purged and the new SATA driver does not get loaded correctly from ROM.
Try this:
1) Delete and empty trash for the following file and two directories:
/System/Library/Extensions.mkext (a file)
/System/Library/Caches/com.apple.kernelcaches (a directory)
/System/Library/Caches/com.apple.romextensions (a directory)