This is for anyone there who is wondering how to make Opera print a page when it spits out the "client-error-bad-request" error (or maybe when it does not print at all).
I indicated xpp as the external printing program (it was xfprint that indicated me this error). When you click on print, xpp pops up. There you have to delete <" "> (without the < and > signs) so that xpp receives stdout. Then you click on print and it prints.
If there is a more elegant way to do this, please drop a line here.