Subversion times out when checking in several files

I have a subversion repository that has worked fine for years. When I now
try to check in several changed files, it times out (apparently when the
network connection gives up after several minutes). I can check in some of
the files individually, including every single one in a subset that failed
when done at once. svnadmin verify passes. I am using a direct connection to
the server (i.e. svn://, not svn+ssh:// ). The message is

Transmitting file data ..................svn: Commit failed (details
follow):
svn: Can't write to connection: Connection timed out

I tried starting the server as svnserve -r /home/svn/SVN/repos --foreground
-X in the hope it would say something helpful, but it doesn't (it just sits
there as if it never received the connection at all). It still carries out
simple checkins correctly (and terminates after every one).

The client is 1.4.6 (default on Ubuntu Hardy) and the server is 1.5.4
(default on Ubuntu Jaunty). It runs over a slowish VPN which does not
appear to molest TCP connections much if at all.

What might I be doing wrong, and where do I start debugging the problem?
Many thanks for any help.
Received on 2010-05-09 18:39:11 CEST