Looking at the data sheet for the OPB IPIF v2.00h, we found out that Virtex-4 was not one of the supported device families. But I think it should be supported as it is shipped with the latest EDK 8.2.
I also found the same issue in the OPB IPIF v3.01c, PLB IPIF v2.01a and v2.02a.
This a Helper Library that supports Virtex - 4 device families. The data sheet will be corrected on the next update of this Data sheet.