Getting Error: The listener returned the following Message: 500 Internal Ser

Hi,

When i assign a single accounts to an customer, it got assigned properly. Even when i tried to assign 150 accounts to given customer by clicking onm add button it got successfully added.

But While assigning a 200 records to a customer i am getting above error i.e. Error: The listener returned the following Message: 500 Internal Server Error.

Could you please have a look into this, why i am getting error when i assign 200 records. Is it java code issue or sever issue please assist on this.

Thanks,
Praf