Sourceforge is a bit ... iffy. Here's a list of things you need to know about our sourceforge account.
Creating a shell
The shell service has the detailed instructions, but long story short: to log onto sf via ssh, you need to create a shell for your username and the project.
ssh -t <user>,email@example.com create
Once the shell is created, it will exist for 4 hours unless closed earlier by the user. Note that multiple logins in short succession can yield authentication errors. Simply waiting 30s between logins usually works around this.