UPDATE: A fix has been applied on the paste.opensuse.org side
paste.opensuse.org currently gets broken by cookies from other *.opensuse.org subdomains and only prints a
Disallowed Key Characters. error message.
It turned out that news.opensuse.org and lizards.opensuse.org send out cookies with a cookie domain of "*.opensuse.org", and one of these cookies breaks paste.opensuse.org.
We'll restrict the cookie domain, but until this is done, you can delete your news.opensuse.org cookies to "fix" paste.opensuse.org. Note that this will only last until you visit news.opensuse.org again (until we have fixed the cookie domain there).
These cookies get sent by more services - we are aware of www.opensuse.org, news.o.o, lizards.o.o, bugzilla and forums.o.o. Follow https://progress.opensuse.org/issues/40025 for more technical details.
This was fixed on paste.opensuse.org