This is probably correct - DDR = double data rate. I.e. it actually runs at 200MHz, but because it transfers data at double the rate of single data rate (SDR) RAM it runs at the speed equivalent to 400MHz SDR - hence it is marketed as 400MHz. The same is true of other DDR memories - 333MHz DDR actually runs at 166MHz and 266MHz DDR at 133MHz.
i.e. nothing is wrong

Somewhere in aida it should tell you the EFFECTIVE data rate, which is 400MHz.