I am using stiff solver Rosenbrock method for stiff ODEs given in numerical recipies book. The program is working accurately for the example equations given in the book. I applied this method to integrate my equations. the program is working well and accurately for certain input conditions. However for some higher values of input parameters y[i], The program is terminating with message " stepsize is not significant in stiff"

I have tried with different step sizes, but in vain.

please suggest how to modify the stepsize "hstart".

Also please suggest what could be the other reasons for the above message
" stepsize is not significant in stiff"