I solved it. The file headers were the reason, because they weren't inserted a comments. Maybe Euclide could check whether the entered text in the 'wizard' is a comment and if not, make it one
When I try compiling a switchboard plug there is another error, though:
** (a:19594): CRITICAL **: file /build/buildd/libpantheon-0.2+r23/obj-x86_64-linux-gnu/lib/Switchboard/Plug.c: line 988: unexpected error: GDBus.Error.org.freedesktop.DBUS.Error.ServiceUnknown: The name org.elementary.switchboard was not provided by any .service files (g-dbus-error-quark, 2)
Can you post the errors you get?