Because of “Enable third-party browser extensions *” (note the *) flag disabled in Tools -> Internet Options -> Advanced tab.
Here is a screenshot 🙂
… of course, you have to check that IE Dev Toolbar add-on is enabled too, this way:
Tools -> Manage add-ons -> Enable or disable add-ons -> IE Developer Toolbar BHO -> Enable
ps: I didn’t run a test before installing IE Dev Toolbar, but seems that NikHilk’s Web Development Helper doesn’t need “Enable third-party browser extensions” flag enabled. sorry for missed test 😦
source: IE Developer Toolbar not working
Technorati tags: IE Developer toolbar, Windows 2003, Internet Exploerer 7, BHO