"WARNING:Data2MEM:47 - Not all BitLanes in ADDRESS_BLOCK 'xxx' have BMM location constraints."
This warning means that some or all of the block RAM instances in the "system_bd.bmm" file do not have location constraints. One common reason for this is that the "system.bmm" file is not associated with the top level of the design. After exporting a design from XPS, the ISE project created has the BMM file associated with "<system>.vhd". If "<system>.vhd" is instantiated inside of another HDL source file, the BMM needs to be removed from the project and re-associated with the top level of the Project Navigator design.