Hi,
You are using a really old version of swat.exe (rev 635, second line in your screenshot). Please update it to the current version to improve results (rev 695). This might help, otherwise, it is very likely that one value of the modified parameters produced a results that is incompatible with the model (i.e. negative flow, which crash the model), so look at the values of the parameters that you chosed
Regards,
Oscar M Cabezas Nivin