Sys is not defined error

I just had my site installed. When I go to the administration area to edit the topics I wouldn't see the topic. The error is the Sys is not defined. It looks like something is missing in the installation. Can any body tell me what went wrong with my installation and  what I should do to fix it. Thanks.

Sys is undefined, it's a javascript error. It has to do with ajax extensions on your server. Is it on your hosting or on local computer?

i have the same problem in version 1.50 in my hosting any body can advice me please

Have you tried this solution ?
http://blog.pantos.name/archive/2007/06/08/264.aspx

In case anyone need it, here I post a solution that worked for me:
(it has a lot of text but you can avoid it and just read the begining)

https://www.nopcommerce.com/boards/t/5503/sys-is-undefined-error-i-cant-add-new-products.aspx#22817