Xilinx bitgen warning
The warning you are seeing is most likely

WARNING:PhysDesignFules:2410 - This design is using one or more 9K Block RAMs
(RAMB8BWER). 9K Block RAM initialization data, both user defined and default,
may be incorrect and should not be used. For more information, please
reference Xilinx Answer 39999.


I just got this warning myself a couple of days ago and looked in to it.  See http://www.xilinx.com/support/answers/39999.html .  Basically, if you are using a newer version of ISE (13.2 or newer, 14.7 is the latest) and you are not using bitstream encryption, you can ignore the warning.  

You really gotta love this sort of bug: they screw up the design, find the issue, and then just change the spec.  "That's not a bug, that's a feature!"