Welcome @swathin
The error is reporting a data issue. There is probably a format problem with the input ligand file, or possibly the terms used for the Strip mask parameter on the form. We can’t see those details yet.
The instruction on the form list out the preparation steps. Doing this in Galaxy would be recommended to avoid technical formatting conflicts. So, if you did this somewhere else and uploaded the inputs to this tool, redoing those steps is one suggestion to try.
If you would like more help, we would need a few more details about your specific job please. You can do this by generating a history share link and pasting it back here for feedback. Thanks! 