module fields not available in process definition

My users are not able to create process definitions based on the Tasks module. None of the fields for this module show up as available for evaluation. I have tried accessing these fields from a process definition based on a related module, but the fields dropdown just sticks at "loading..." The Tasks module works fine otherwise, including with various post-save hooks I have created. I have checked my Vardefs, which look fine, and so I am stuck. Any suggestions?