Router changed to open network - ipad still asking for password?

[Stevemon]

I had my ipad2 connected to a router ok with wpa password. That particular network has now been changed to open ( no password required ). I changed wifi settings to forget that network, then found again, but still asks for password. Will not let me login without entering something (join button greyed until something entered) and the old password will not work (as expected). I have tried reset of network settings, same results. Has anybody come across this and how do you get passed it.
By the way, other devices that were previously password connected have joined ok without a password.
Thanks guys & gals