When doing a local check, the first registered socket seems to be blocked forever.
(I suspect a connection to bug 788 (http://bugs.openvas.org/788)
I digged into the code but the origin stays unclear for me (messages in the following extract stem from
openvas-server/shared_socket.c)

ssh -v on the target responds:
OpenSSH_3.5p1, SSH protocols 1.5/2.0, OpenSSL 0x0090609f

/var/log/openvas/openvasd.messages shows ("xyz" are sane values):
...
[Wed Feb 11 09:57:33 2009][25572] user xyz starts a new scan. Target(s) : xyz, with max_hosts = 20 and max_checks = 4
[Wed Feb 11 09:57:33 2009][25572] user xyz : testing xyz (xyz) [26846]
[Wed Feb 11 09:57:42 2009][26846] shared_socket: Secret/SSH/socket is unknown
[Wed Feb 11 09:57:44 2009][26846] shared_socket: Secret/SSH/socket is unknown
[Wed Feb 11 09:57:45 2009][26846] shared_socket: Process 26888 registers a shared socket (Secret/SSH/socket)
[Wed Feb 11 09:57:45 2009][26846] shared_socket: Secret/SSH/socket is busy (locked by 26888)
[Wed Feb 11 09:57:46 2009][26846] shared_socket: Secret/SSH/socket is busy (locked by 26888)
[Wed Feb 11 09:57:46 2009][26846] shared_socket: Secret/SSH/socket is busy (locked by 26888)
[Wed Feb 11 09:57:47 2009][26846] shared_socket: Secret/SSH/socket is busy (locked by 26888)
... continues like that ...

Date: 2009-04-23 10:25
Sender: Chandrashekhar B

Closing the bug as most of the plugins performance has been enhanced
now. If there are any plugin which is still holding the socket
for longer duration, please report a bug on that particular
plugin.

Date: 2009-04-17 15:53
Sender: Chandrashekhar B

Since ssh shared socket behavior is implemented, slow plugins
cause the other plugins to wait. This can be closed since we
enhanced the performance of the most slow plugins.

Do I?

Date: 2009-02-12 11:09
Sender: Felix Wolfsteller

Seems to be linked to (an?) individual plugin(s):
... 90000 (ClamV), 90014 (Mozilla) or 90029 (OpenOffice).
In the setup, a large number of NVTs were not present,
including some .inc's and others that one of the three nvts
mentioned above possibly depends on.