try downloading the rs client under the downloads section. This might help, i have a mac so i can't play on the browser so i have to use the client although I'm not sure, gl trying to fix it!
thats happned with me be4 all u have to do is use internet explorer if that didnt work delet the new V of java and download the one be4 it and this should work
I have RS client and its sooo laggy and glitchy. Whenever I open it, my whole screen flashes O.O As for your problem... I'm not sure how to fix that. Sorry :/
I don't understand dutch, but maybe try reloading the page, if it doesn't work, i got a junk cleaner, sometime computer gets slow or won't work because of lagg.