If the fitting exercise does not get started, there are a number of potential causes:

1. There is some error in the model. Check all inputs and verify that the model runs in Simulator.
2. The fit is not improved by changing any parameters; this could be due to:
   1. Poor initial guesses for parameters (e.g. very low or high values such as 1e-10). Run the model in Simulator to find parameter values that begin to have some effect on the fit (manual fitting).
   2. Inappropriate selection of parameters/data for fitting. Check the model and make sure that the parameters selected will affect the corresponding model calculations of the data series selected. Run the model in Simulator to check this.
3. The model runs very slowly. Check this in Simulator. Click here for further help on slow-running models.