Unable to view notifications waiting for response at a perticular user end

Hello,

I want to see notifications waiting for the response at the particular user's end. When trying this i am getting following error:
Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

The navigation path is followed as:

sysadmin > Workflow Adminstrator Web Application > status Monitor
Workflow Type: Ap invoice Approval
Internal Name: APINVAPR

Click on more options:
Select
Waiting for response from : Users and employees
selected name of employee whose notifications i want to see. but after few minutes buffering its prompting above red light error.

I would really appreciate your response on this.