Weird problem with RreeView control under IE 6

[Mark]

Hi, I have a treeview control which I populate with info from a database.

When I click on a link in IE the link does not post back but instead opens a
new browser window with

javascript:TreeView_ToggleNode(treeNav_Data,6,treeNavn6,'t',treeNavn6Nodes)

in the address bar!

The app works fine under Firefox!

Any help appreciated
Thanks
Mark