What does this mean? And how do I solve it?

* Fatal error: error in assign: Nonstandard chemical bonds are found on atoms  such as VAL199:N, which cannot be typed by the selected forcefield.

I just docked my ligand and I performed in situ ligand minimization but it always says that. If I change my forcefield, will it not affect the quality of my results? I have always used CHARMm forcefield all through out my docking procedure. :\