edit address redirects to 404 error

Hi,

That's really strange. The 404 error does not only happens there but also if you take the link of the 1 step and open it manually.
Once you are on the checkout, change your payment method.
The URL will be:
ipcfix.com/store/checkout/step/step-1

If you try to open it in another tab, it won't work.
That should however work since it's the same URL you have on the other page. That's the cause of the address edition problem.
It's a SEF related problem. Could you try to deactivate SEF on your website and try again ?
What are the URLs ? Does it work ?
Do you use a specific SEF component ?

There must be something else on your website which causes that problem when SEF is turned on as other users with SEF turned on don't have the problem.

I would start with your 404 redirect extension since it's linked to URLs. So you should try to disable it.

So on the other website it works with that 404 extension and SEF on ?

What other extensions/plugins do you have installed on your website ?

I don't see any extension standing it in your screenshot.

What would be the system plugins that you don't have installed on your other website ?

If you unpublish them, does it work better ?

What a re the SEF and non SEF links of the address edition iframe (you can use firebug to get that information once the popup is openned)?