FFT MegaCore Function Generation Stuck

Hi,

I was trying to generate a 1024 point Variable Streaming bi-directional FFT IP Core using the FFT MegaCore Function. After click "Step 3 Generate", it will hang in there forever. It shows that the function stuck at "Generating MegaCore function top-level". The screen shot is attached for your reference. A temp folder has been created named "iptb_fft_temp4719569924717944842", which contains some .v files and .hex files as well as some ".m" files. Do you guys have any idea what causes this stuck? I have tried more than 20 times, and only successfully generate the .qip file once. Any inputs are welcome.

Thanks

-Roger