How I fix in Isa Server 2006 the error code: 504 proxy time out. The conection time out 10060 ?

The problems is when the all clients that  try to access the page https:\\onevoice.1199.org or citrix.cosvi.com is connected and in the day this is disconnected, and you need to wait more than 5 minutes then you can connected to this page and the problem continue all day.  The message tha receive the clientes is error code: 504 proxy time out The conection time out (10060). To check this problem I create Isa server 2006  In the dashboard , logging  I create query to analize an specific client ip to see what happen when  try to enter the https page.  I start a query and see the information that say the rule that permit  to protocol https to the port 443 failed the conection. I dont have this problem in July, this begin in August  we didn' t any changes to isa rules. We has the isa server 2006  in Windows Server 2003. How I can fix this error ?