as the lads have said do it in spring, the joints just will not dry out enough to seal properly, i saw a lad sealing a drive the other day it was a discrace. the sand was all over the blocks and half the joints were empty of sand and then he sealed over the lot. if it was my drive i would want the lot ripped out and re layed. its ruined!
i beginning to wonder myself whether to stop sealing drives, i use resiblock and do a great job but its all the hassle of buying the stuff in, waiting for the weather, then there is always the risk of comebacks.
anyway good luck!