[Plugin: WPListCal] Add media doesn’t work??

I had this problem also, it looks like the stylesheet for thickbox isn’t being pulled in.

I don’t know an awful lot but I’m assuming the functions required to pull all this stuff in have changed in WP3. Looking at other plugins with similar problems I followed the steps here: http://wordpress.org/support/topic/310339

And now the thickbox seems to load.

That worked for me, thanks