probleme when fitting DDR2 DQ : critical warning

Hi,

I am trying to map a cyclone IV with 3 DDR2 :

- fpga = EP4CE30 F484

- DDR2 micron 512mb x16 (MT47H32M16HR-25EG)

I both try manual and automatic assignment but I always have this critical warning :

Critical Warning: Fitter could not properly route signals from DQ I/Os to DQ capture registers because the DQ capture registers are not placed next to their corresponding DQ I/O

What does properly means ? do I have to remove this wrning and how ?

thanks.