Internal time step error

Hello

I am designing a 4 port Anisotropic transmission lines in HFSS.

I imported .s4p files from hfss into ADS and i am running simulation with IBIS TX and RX models . In the transmitter section i have kept PRBS frequency to 30gbps . I have included channel simulator. When i simulate the design i am getting an error " Internal time step too small at time 4.64e-10s".

I am unable to solve this error. can anyone hep me with this?

Thanks in Advance
Srikanth