This definately sounds like a loop in your network. It can sometimes be caused by very low timers, but in my experience loops are the major source of this error.
We recently had a similar problem with a service partner who, and your not going to believe this, put a cross over cable between two wall outlets that connected to the same switch. Due to a missconfiguration port security had been taken off the switch, so the port allowed the connection. This looped the entire Vlan and sent our distribution switch CPU up to 100%....
I would start to audit the CPU of all your switches that have this Vlan on it, if it is a loop the access switch with the highest CPU will probably contain the culprit.
