RIBX errror when running coupled model (WRFv4.1.1-CMAQv5.3.1)

Hi all,

When i was running two-way coupled model (WRFv4.1.1-CMAQv5.3.1) for January, Apri, July and October, my run aborted with the following error:

“-------------- FATAL CALLED ---------------
RIBX never exceeds RIC, RIB(i,kte) = NaN THETAV(i,1) = 290.1336 MOL= -280.1879 TCONV = NaN WST =
NaN KMIX = 2 UST = 7.6713055E-02 TST = -1.3038928E-03 U,V = 0.5312256 0.7183169 I,J= 11 68

For July and October, coupled model have successfully completed the whole month simulation without any error, but for the January and Apri the model run was aborted with above error. I also tried with a smaller time step (30,60,120 and 180), but the problem persists. I also changed the initial and boundary conditions from “NCEP FNL” data to “ECMWF" data, but the simulaiton still crashes afther 3-4 hours of simulation time.
And i am sure that all simulation were performed with same namelist.input at the same server.

I would appreciate any help on this issue.

Best wishes,