creating testbench in qsys

hey,

i can´t create a testbench of my qsys system. even when i try the project of tutorial an351 it fails with the message:

Error: nios2: Failed to generate module niosii_system_tb_niosii_system_inst_nios2

anybody knows a solution to this problem ? i´m using quartus II 11.0.

thanks for helping guys..