from your description, i would interpret your problem in the following way:
1. growFactor is a variable defined in your model, initialised to a value either within your omi file or a steering file read during model initialisation.
2. this variable can potentailly be adjusted every timestep that your model performs.
3. after a few timesteps the value of growFactor is going out of its permissable range (1 - 10).
if this is right, it suggests that while the initialisation has probably occured ok (because you are performing timesteps before getting the error) but that an illegal value for growFactor has been occured during the simulation.
without seeing your code, it's difficult to know where this might have happened, but two places to look would be:
1. the values of the variables used to calculate growFactor. possibly one of these has caused your model engine to blow-up - perhaps check that all the values passed into the model via steering file or omi file are correct and will run in a standalone simulation and that they are getting initialised correctly. to do this, worth checking the values at the end of initialisation?
2. the call being made to the dll (in compute) may not be quite right - how are you using the dll? are you shutting down the model engine at the end of every call and reinitialising it with the updated values? or are you keeping the engine running but returning without shutting down? depending on your approach, there are different things to look at.
hope this helps - if not, feel free to email me your model and i can take alook for you.