We had this problem when using the ssh+svn://email@example.com/repo syntax for our subversion server. Because it was so obscure we thought it would be a good thing to post it here incase anyone else had problems with it as well.
Related to windows XP when using TortoiseSVN /w putty.
It was found that errors such as "Connection closed unexpectedly" if you had a misconfiguration with putty when trying to do a svn update.
1. You have svn setup properly and it stops working after working with putty settings.
2. You are using either TortoiseSVN or the built in SVN client with cygwin.
You randomly have SVN stop working or try to connect to the wrong server when you are attempting updates/commits/etc...
It seems that if you have anything but a blank box set for your "Default" profile in putty it will cause errors. When doing a SVN update it will appear that the client properly connects via ssh to your remote server --this is true-- if you check your server logs you will see a successful login but that it also closed almost right after it opened.
1. On your windows box open putty.
2. Locate the "Default" profile and click the "Load" button with it selected.
3. Delete anything that loads in the "server" section. Leave port set to 22.
4. Make sure that "Default" profile is still selected and click "Save".
5. You should not be able to run updates/commits again properly.