Due to maintenance works, the nightly server will not be available until mid-august. During this time, no nightlies will be created.
(Announcement on the german forum (http://www.simutrans-forum.de/forum/index.php?page=Thread&postID=95752#post95752))
Translation courtesy of DirrrtyDirk
Thanks. I began to think if somebody is on holiday.
I guess that it is mostly due to changes on SVN server, sf.net.
The nightly server is back and compiling again. (Link to german forum post (http://www.simutrans-forum.de/forum/index.php?page=Thread&postID=96513#post96513))