CRC (cyclical redundancy check) error checking was introduced with UDMA modes. As Ian has stated, if frequent errors occur the transfer rate may decrease to a slower mode.
I know of no absolute fix for this problem, but two things that may make a difference:
Use a 80 wire IDE cable and not a 40 wire cable. The extra 40 ground wires in the 80 wire cable should enhance the signal stability by decreasing crosstalk between the adjacent 40 signal carrying wires. This could improve the CRC error rate.
Use the shortest cable that will work with your setup. 18 inches is the longest length permissable under the specifications. Using the shortest length that will fit will improve overall signal integrity. NewEgg
has round IDE cables starting at 10" in length, but be sure that the cable is no longer than 18" in length.