I have two s5 115U cpu 944 (6es5-944-7ua21) unit. I can not go online with step5 v.7.1. I have an old simatic PG605 and I can program both unit without any problem. What is more interesting is that I don't have any problem communicating with other cpu's (943, 944b, 945) using step5 v.7.1. What could be the reason?
There are machine has same plc in my factory. I could not be onlie like you but but also other plc's and same type of plc in other machine are OK. I asked one of siemens officer about this problem. he said me " Producer of mahine don't want anyone to change programs in plc by online. So they may destroy port of plc."