Hello Holch,
thanks for your answers. After I updated I immediately send some invitation without any problems and loged out. I started to wonder that I got no conformation mails and logged in about 2 hours later and wanted to send a test invitation. Then I got the failure message.
I went to global confoguration and saw the disappeared setting. The setting is SMTP, but still the fileds are grayed. I attached a screen shot of that page (in Finnish

). I didn't do any changes, except updated from 2.00 to 2.05 version 140302.
I just tried to save an other email method and go back to SMTP, but still the fields stay grayed.
Strange is also that ending of my admin email address has been changed from .com to .de. The server name ends .de, but I use my .com email address.
I have an other "test version" of limesurvey with version number 140226. There everything is going very smooth.
I hope this problem is to solve and I'm very thankful for every solution try.