Server Error on class update

Company - LONG

Server - LB

Employee - Blank Daniel

Step:-
1.Login to application using partner credential
2.Click on Apply Classes and Payroll Schedule tile
3.Select Class A , Class A and Payroll - Monthly
4.Set Effective - Yes and Date - tomorrow - 05/12/2017
5.Search employee
6.Select same employee and click on Apply

Actual - Server error on page

Expected - Classes should get's changed

CC - Saurabh Sablaka