By the message that you have, I can recommend that you will need to review the performance of your server.
An excellent tool is the governance dashboard, here you can see the performance of your server, what is the which is the dashboard more big and what is the performance in the server, how much of memory ram that the server consume.
Other excelent tool is the QV_Utilisation_Reporting.qvw and the QV11SystemMonitor.qvw
The next document give you the best recomendations for configure the server
I hope the information can be usefull for you