Hi I have joomla 1.012 with virtuemart 1.08

installed joomsef-2.2.6 with virtuemart extension

The urls are looking perfect on all pages and products. BUT when I add a product in the cart and click CHECKOUT
I get this message: The page isn't redirecting properly...
and this is the end of the story...
Any idea how to fix it, I really need this. Actually it does on other sites of mine too so probably could be a simple fix...
Thanx very much...