"Page name is missing" when trying to edit wiki page

I try to edit e.g.

http://planetx.cc.vt.edu/AsteroidMeta/HomePage

by clicking on the "Edit this page" link

http://planetx.cc.vt.edu/AsteroidMeta/?action=edit;id=HomePage

but what comes up is the page

http://planetx.cc.vt.edu/AsteroidMeta/?action=edit

with the error

"Page name is missing"

And this same error comes up if I supply the correct URL by hand.