WEP works but "unable to Join" on WPA / WPA2

[eske]

I have an ipod touch 2nd gen, that just won't play nice with my Zyxel router with WPA-psk or WPA2-psk encryption

it will connect if I use WEP encryption so i know it's not the wifi card

but I have other devices on my network that don't like WEP

and WEP is considerably less secure

so at the moment every time i want to connect i have to re-config the router

I have scoured forums looking for a similliar case but have found no sollution
it's not a case sensitive password issue,
I have hit "forget network" and tried to re-login,

but I can find no solution

any ideas?