07KT97 PLC PLC class 3 error

I face problem in one project with ABB 07KT97 PLC PLC class 3 error always appeared on HMI disply, and i can not go to PLC configuration in online mode to find the reason of the problem.
Please help regarding this issue.
--

Do the PLC work ?

If I remember right you have to reset the "error" to get led to turn off. But if you PLC works why bother ?

Do you have the manuel ? if not http://www.google.dk/url?sa=t&source=web&cd=2&ved=0CCAQFjAB&url=http%3A%2F%2Fwww05.abb.com%2Fglobal%2Fscot%2Fscot209.nsf%2Fveritydisplay%2F169cfc297a54df11c1256df20044947d%2F%24file%2F2cdc120066m0202.pdf&ei=3T3tTayKIYXNsgan8d3nCg&usg=AFQjCNETg_RsqxO1qulX6UYp8t3DQSiZBw&sig2=AN-OlwOyFuvEEQMJ_3xSjg

See page 7-1

And you problems with go online has nothing to do with the Class3 error (light error)