Data sensitivity tends to suggest some sort of bus collision or ground bounce. It could be the SanDisk are faster than the other devices - thus causing the issues you describe. I dare say the SanDisk works ok in a PC or usual IDE interface. If you're using a CPLD - watch out! These things are damn fast and it is easy to get glitches of a couple a nanoseconds - I've been bitten before! Also, if it's a handfull of ttl (hc...) calculate your delays - propagation and buffer enable/disable. The fact you can write ok also suggests buffer enable/disable issues. Say you're using the select line to also put the data buffer into read - the SanDisk logic may be faster and is trying to drive into a brick wall whilst your data buffer decides to turn around for a few nanoseconds. The solution here is to do some calcs and delay the select to the compact flash by the required amount.