Error message when searching two words or phrase in OpenMx Forum

This is a bit meta, but when I search for more than a single word using the search function on this website or the advanced search function of the forum (restricted to the forum), I get an error message:

"Forbidden

You don't have permission to access /search/node/TERM1 TERM2 on this server."

Google doesn't seem to search the posts itself but only the forum overview.