I have the following issue on a customers Proxy Server:

NW6 SP5, BM3.7SP3 with field Patch 4c

We change the ISP and now we have a DSL Account with static IPīs. But if i connected to this ISP i get the 504 Gateway Time Out error Message - Ping work, directly connected Workstation work, NAT work only the Proxy doesnīt. If i use the old ISP (T-online) erverything works fine.
I tried TID10090509 an the ISP change the MTU size to 1500 -> without success