linking netgear extender to technicolor router

My service provider has given me a free technicolor tg589 router to replace my old existing netgear router. i have been using a wn3000 RP range extender which has worked with the Netgear router for a number of years. Have installed the new router, set SSID and password via a connected PC , reset extender to factory settings, synchronised extender to router, all four green lights have appeared on extender. However when I connect a device to the extender network (aaaa_EXT) it asks for a password. When i type in the password that I have been using and the one I set up for the Technicolor router it says it is incorrect. I have tried the password and wireless key on the plastic card which came with the technicolor router but it still says it is incorrect. Have contacted service provider who says everything looks correct and cannot help.

 

It appears that the extender has  acquired a new password