Minecraft 18w11a server not starting

When I try to start the 18w11a server file which is named server.jar with the start.bat the server starts up and displays the text which is also in the latest.log! Exept that nothing happens. Also the server started the first time, but now it only works if I start it with the nogui argument. I deleted all files exept server.jar and start.bat but it makes no difference. If I run it as Administrator it tells me Error: Unable to access jarfile server.jar. I have no Idea why it does that.