[otrs] forced logoff and error webpage

Hi, I have a question about my OTRS ver. 2.3.4 installed on a Windows machine. When Agents login after an unspecified period of time they disconnect unexpectedly or a message as "Internet Explorer cannot display the webpage" appears. So I have to refresh the webpage e login twice. In the Sysconfig of admin console I' ve checked SessionMaxTime and SessionIdleTime but are rights (default values). Please help me. Thanks Alessandro