I took a look at Tasque on the gnome web page. It looks like it requires a lot of mono bindings plus GConf. So I'm going to take a stab in the dark and assume that it is trying to read your browser settings from GConf.
I ran into an issue with gwibber where it couldn't open up a browser because I had upgraded firefox since I had initially installed GConf. So that may be a reason why it is not reading any browser association set in KDE. Can you report the output of this command?
Code:
# gconftool-2 -g /desktop/gnome/url-handlers/http/command
Also, is your current browser version the same as the one that is in the output of the previous command? Again I'm just guessing.