MarketPress Checkout button throws 404 error…(?)

Hi All,

Have installed Marketpress 2.4.2, GridMarket 1.4.8, added products, theoretically fired up paypal… but during testing :added products to the Shopping Cart, but upon clicking the CHECKOUT button, it throws a 404 error…

I do have it installed in a subdomain … will this mess it up?

Also, Paypal never asked for the url (?) <;

Any help would be appreciated.

As always THANKS!