This error can occur due to several reasons:
- Your function might be creating a singularity or any other discontinuity (with an Inf or Nan result) at the specified time. You can determine this by examining the output of your ode23s call. You can plot the output obtained (all columns of the result as functions of your independent variable) and check for singularities.
- It could also be that your error tolerances are too tight. You can loosen the tolerances using odeset function.
If you still dont get a reasonable solution, try using other integration solvers. Try checking your code once again to make sure there aren't any bugs. In case your system is poorly behaved, consider changing the model you're solving.
Hope this helps!