ed some help, please. I set all my GPUs on one worker. It doesn´t help. I still have a lot of invalids. I´m mining on the EU pool. Are there some problems with the server?

At the moment:

10 Minute Hash Rate 5907 Kh/s
Valid Round Shares 13056
Invalid Round Shares 9024
Your Efficiency 59.13%

Edit: I even tried dif. of 16 and 32. It´s worse. Between 64 and 256 is no difference.