I think this problem appeared recently because i've not notice it before.

Investigated that by default IE8 has an option "Compatibility View" is enabled for a inranet sites. Usually Zabbix web interface hosted in the local network and because it will be automatically defined as the inranet site.

As result many of pages has JS errors (even login page) and web interface almost doesn't work.

We need to disable such IE default behavior.
Go to: "Toos" -> "Compatibility View Settings" and uncheck option "Display intranet sites in Compatibility View" and press Close.
The page will be reloaded automatically without errors. That's all.

After press Close button, on right from address bar a special button "Compatibility View" appears and a manual mode will be available. Before this button was hidden because of automatic mode for the intranet sites.

So, we need to document this as note in some place(s) of 2.0 documentation.
Suggested pages:
1. http://www.zabbix.com/documentation/2.0/manual/introduction/whatsnew200
2. http://www.zabbix.com/documentation/2.0/manual/appendix/faq

or maybe you can fix this