Unable to add product to cart after upgrading

[Sophia(sofi)]

I checked through out trying different solutions given through out the forum 

 

In my error log I get this error 

 

Undefined index: product in public_html/tools/smarty/sysplugins/smarty_internal_templatebase.php(157) : eval()'d code on line 74

 

 

Please someone help me urgent 

 

My site is theethnicstory.com 

 

After upgrading all my files are working fine except this issue, which has stopped all shopping  on my site.