MartinCh, haven't read your posts too carefully but if I understand you correctly you tried to print your boarding pass but it had not appeared on screen and there is an error message per your picture?
I have seen this a number of times - there is a long-term glitch in Ryanair's software which means under certain conditions the boarding card does not appear below the top section of the page you have shown.
The workaround is to go back / login again with your email address and flight date/destination detail and choose the "Reprint" option which you have alluded to.
Don't ask why, it's just something that happens often enough to confuse the hell out of some people
