[horde] Cannot write to cache directory /tmp

[Simon B]

Hi.

Since yesterday's git pull, I'm not able to access any modules..

The horde log is filled with:
2013-06-03T08:54:41+02:00 WARN: HORDE-BETA [imp] PHP ERROR: feof()
expects parameter 1 to be resource, null given [pid 25543 on line 4190
of "/usr/share/git-horde5/framework/Imap_Client/lib/Horde/Imap/Client/Socket.php"]
2013-06-03T08:54:41+02:00 WARN: HORDE-BETA [imp] PHP ERROR: fgets()
expects parameter 1 to be resource, null given [pid 29060 on line 4203
of "/usr/share/git-horde5/framework/Imap_Client/lib/Horde/Imap/Client/Socket.php"]
2013-06-03T08:54:41+02:00 WARN: HORDE-BETA [imp] PHP ERROR: fgets()
expects parameter 1 to be resource, null given [pid 25543 on line 4203
of "/usr/share/git-horde5/framework/Imap_Client/lib/Horde/Imap/Client/Socket.php"]

The browser says

Cannot write to cache directory /tmp

But /tmp is owned by www-data

Any ideas?

Simon