Solution:1
Did you update to WooCommerce 3.0? Make sure the theme you are using is compatible with WooCommerce 3.0. If it’s a plugin you are using for Paypal disable it first and see if thats the one causing an issue.
Seems like some incompatibility.
Solution:2
ok, the problem was solved by re-uploading all Woocommerce files over existing files on server.
Solution:3
This seems to be the plugin / theme conflict issue and to be honest cannot be judge directly.
However, there are some primary steps which you can follow, as below :-
After this check by following same procedure.
Let me know if I can help you further…