decode my update error

[eddski]

can anyone help with my update error:
W: GPG error: http://us.archive.ubuntu.com jaunty Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>

not sure what this means, but i cant update.
thanks in advance

ok so i went back and cleared the error box and my updates came through
then its is sporadic, what gives?

[nhasian]

seems like its having trouble contacting the server. try switching to a different server in system-> administration-> software sources