You could ask here - but you'd need to supply more info.
That said, it sounds as though something in your infrastructure has changed. My first suspect would be the IP address of the branch that's no longer connecting.
Can you PPTP/IPSEC to the failed branch? When you do that' are you using an IP address or a FQDN? Is it the same FQDN used in the IPSEC tunnel?
FWIW, dyn.com has recently discontinued its free dynamic DNS service. If you were relying on that to convert a dynamic IP into a fixed FQDN, then the next time your IP changed, things would stop working. Timing's about right for this to be the issue.