Upgrade to 1.9.1

[sgseforim]

Hi, I just upgraded to 1.9.1. Before the upgrade everything was working great for nearly a year, now after the upgrade I have several problems:
1) In Internet Explorer, when I click "Add to cart" the page refreshes as if it is going to be added to cart, but then it doesn't add to cart.

2) In Chrome, the item will be added to cart, but it doesn't allow me to click on the cart icon.

Any ideas?

[JLHC]

Can you check if the file permissions are set correctly? 

A Magento upgrade through the Magento Connect Manager can cause file permissions to be reset wrongly to 666 (which is insecure) while most servers can only accept up to 644. 

[Suma Tata]

Again you have to replace 1.9.1 version js files then every thing works.