Oracle 10, Apex 3, PDF printing and ORA-20001

I have been struggling to get Apex 3.2 to print PDF, using BI Publisher.
Time and time again, the developer reported he got the -by now- dreaded error:
"ORA-20001: The printing engine could not be reached because either the URL specified is incorrect or a proxy URL needs to be specified."
Because I spent quite a lot of time researching this, and the solution was so simple, this entry.
Please be warned: this error is to be expected when using 11G and the database listener.
This error also seems to manifest when you use the defaults, which do not seem to get accepted; instead: fill out the fields (with Print server host address 'localhost' and port '8888')

In my case, however, it turned out to be a space, following the port number.
Hope this helps somebody to save some time...

Edit: see this entry for setting this up in a run-time only environment.
Edit: see this entry if you run into an ORA-20001 with Oracle 11G