Adding extra switch freezes entire network

Well I finally figured out what the problem was and have stopped the network freezing and hanging all the workstations for anyone else that finds themselves in that position when trying to add a managed switch. It turns out the the Netgear switches I have cannot handle having multiple machines with the same bridge priority value and let the supposed smart switches figure out which one wants to be the root, instead I had to offset each switch so no two switches had the same bridge priority value then they were quite happy to all interconnect. Lesson: do not reply on the Spanning Tree Protocol to sort itself out across multiple switches, set everything manually. It also made a difference to set BPDU to filtering rather than flooding and each port authentication to multi session. With those settings the network is kicking butt!