Macbook drops despite correct password

[#1]

Hello and good evening,
So my tg585 v8 arrived a week or so ago. we have a PC (Windows) and iphone and a macbook air - all of which i want to connect to the new network.
suddenly the macbook and the iphone started saying 'invalid password' even when i knew it was right.

a wiseman on this forum said it may be that the wireless SSID name plusnet gives out is too long so i shortened it but kept the same wpa + wpa 2 encryption.
this solved the problem for the iphone (and the PC has always worked)
but the macbook is still being problematic and sometimes takes many goes (after saying 'invalid password') to connect.
if anyone has an idea on how to solve this I'd love to hear from you
thanks in advance.

[#2]

Insist on Plusnet fixing it for you.
Try to get Technical support to fix it for you.
In desperation you could try a different router, any different router as the Thomson is rubbish.

[#3]

It's probably worth getting the firmware upgraded on the router - if you have a windows PC available you can do this from there, but unfortunately there's no way of flashing from a Mac as things stand at present. If you only have Macs available let me know and we'll arrange to get it updated remotely for you.
If you do have a windows PC the details on upgrading are here: http://community.plus.net/library/hardware/how-to-upgradedowngrade-the-firmware-on-the-thomson-585v7...