This is an issue with CompXLib . When both of the languages are used, CompXLib will only compile for Verilog and not compile for VHDL.
Always compile using the "-w" switch. This will overwrite the libraries, allowing you to work around the problem.
This problem has been fixed in the latest 7.1i Service Pack available at:
http://support.xilinx.com/xlnx/xil_sw_updates_home.jspThe first service pack containing the fix is 7.1i Service Pack 2.