"Error executing query"

I have installed Webcalendar 1.1.6 and the appropriate version of Webcal for 5.x. Installed Webcalendar and was able to view the calendar as a stand alone app.

I followed meticulously all the instructions for setup of the webcal module, have double checked all settings and emendations I have made to files.

When I go the webcal in my drupal site, I get this message:

Error. Error executing query.

Any ideas why this might be happening? Thanks very much.