Error: can't place pin mem_dqs[1] to location T8.

I face this problem before. You have to do some setting because there is too much bidir pins for 1 Vref.:)

1st :

Assigment-Device-Device and Pins option-Dual purpose pins(set all value to: use as regular I/O except for DClock&nCEO.

2nd :

Assigment-Assigment Editor- Change all DQ,DQS and DM pins to (Output Enable Group). For the Value column, set any number same for those pins.

eg: DQ[0]->Output Enable Group->123456(Value)

3rd :

Assigment-Pins(Change IO standard for all DDR related pins to SSTL-2 Class I.)

You now are able to compile without any fail hopefully. I face this before and want to help you.:o

Thank you:

Shahril