Just ignore it - it's an SSL certificate warning that we'll have fixed ASAP (we updated the certificate a month back, but it looks like it wasn't done correctly so we've got to do it again).
As it is no-one's Swellnet accounts have any information of value (we don't store credit cards, or anything like that) so there's nothing to worry about. Just really an annoyance when logging in.
Apologies for the inconvenience.