Hardware Error 81 is what you will get if the region stored in the flash RAM doesn't match the region of the cartridge. One of the common reasons for this error when you do have matching boards and carts is that someone cut the power while the game was doing it's initial load after changeing cartridges. The way the new cart is flashed into the RAM is by first erasing all the existing information (including the region code) and then loading the new code in. The region code is apparently one of the last bits of information loaded into the RAM so if power is cut before the load is completed the mainboard is toast.
You can remove the LH28F008SAT-85 flash RAM at location U1053 and change one of the bytes to a value matches the region code value from the cartridge if that is the reason for it. I am pretty sure channelmanic has fixed some of his boards like that.
I have two SP1 boards with that error, I just haven't gotten around to trying the fix (complicated by the fact that I don't have the add-on for my Q4X programmer to do TSOP flash RAM).
*Edit*
I just had a thought, check to make sure there aren't any bridged pins or shorts at U1053 and U1054. Those are the two chips that the game loads into. If they are good then my money is on needing to reflash U1053.
Brian.