Can't Checkout - Checkout redirects to Shopping Cart Home

OK - so a customer just reported this, and we haven't updated or changed ANYTHING on our site in quite a while ... running 1.3.8 ...

Been working fine - now, all of a sudden, any attempt to checkout redirects you to our homepage.

You can add products to shopping cart fine, but when you click the checkout button (which should take you to https://www.mckinnonoutdoors.com/checkout_shipping), it just redirects straight to the homepage (http://www.mckinnonoutdoors.com)

Again, we've not updated or modified any files in a long time, so I'm not sure what's causing this, unless there is a shipping module or something that is disrupting it? (we're using the UPS module)

Update: disabled our UPS module, just to make sure that wasn't it, and had no impact.

Might not have anything to do with checkout process, your log in link doesn't work either.

I'd guess your SSL isn't set up properly. Try turning it off and see if those pages work.

Turn off your SEO/rewrites ... does it start to work properly now? :unsure:

Ajeh,
That was it - I disabled SEO and it works.

Here's the weird thing, though ... my webhost was able to login and place 2 orders WITH the SEO plugin enabled ... so why did it work for them, but not for anyone else. I'd like to keep the plugin enabled, so any input on what the server-issue could be that is not liking the rewrites, that I can relay to the webhost?

SEO/rewrites are weird creatures ... they could of hit your site in various locations where things worked while other areas did not ... not really sure without sitting down to see how they did it ... :unsure: