In the previous version of Vivado, the axi_7series_ddrx core was created in the MT8KTF51264HZ-1G9-1.5 SODIMM but is no longer listed. This is because previously MIG only supported the 1.5V SODIMM, but now it also supports 1.35V, so the -1.5 suffix has been removed.
To work around the failure, edit the MHS file and remove the "-1.5" suffix, then try again.
Revision History
10/16/2012 - Initial release