JAMES VAN DER BEEK was hoping to have a "Dawson's Creek" reunion on his new show "Don't Trust the B---- in Apartment 23", but KATIE HOLMES and JOSHUA JACKSON turned him down.  Supposedly, the Beek was "bummed."

An "insider" tells "In Touch Weekly", quote, "[Katie and Joshua] are too busy . . . they have a million things going on in their careers."