Valence Checker - error message

Hi

I've processed my compounds through molecule to indigo without any errors.

However, when I then attach a Valence Checker, I get this error

 

 Execute failed: array: invalid index 0 (size=0)

 

Any help on what this means would be great. I've not changed any of the features except Write Files To Disc as I am processing 1.3 million molecules.

 

thanks

 

Louisa