Cannot perform ‘=’ operation on System.String and System.Int64

This error usually occurs when you try to compare a Integer with a string type .
Please check in the workflow , the places where you have made data comparison .

In most scenarios when we use and implement filter criteria , the data in the datatable is of type integer & comparison is of type string .
Assume your scenario could be different .
Due to incorrect datatype mismatch , the workflow runs into exception .