function call in simulink

i wish to load my mfile function into simulink model block of "user defined function". im just defining 4 input channels, two functions are processing to generate some matrices, i have checked these matrices are being produced but the output equation is the combination of these matrices and the input. but when i run the model, it displays the message of error and indicate that there is some singularity and suggest to minimiza step size and tighten the error limits. in my simulation settings, all is auto, im unable to understand, why is there singularity error in solution