Multiple GCal permissions/header errors with Appointments+ (development site, non-root domain, share

I'm getting errors on the front- and back-end of a site I'm working on when trying to integrate Appointments+. I think the error might be because the site's not currently at the root domain, it's a dev site using a subdomain on a shared server.

I've also tried disabling all plugins and enabling just Appointments+, then enabling WPMUdev Dashboard and App+ together but I get the same errors each time at the top and bottom of the page:

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HEADER:
Warning: session_start() [function.session-start]: open(/tmp/sess_fd45b1589e0d14d2adf35d327cbc8da6, O_RDWR) failed: Permission denied (13) in /home/pwcakes/public_html/wp-content/plugins/appointments/includes/class.gcal.php on line 36

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/pwcakes/public_html/wp-content/plugins/appointments/includes/class.gcal.php:36) in /home/pwcakes/public_html/wp-content/plugins/appointments/includes/class.gcal.php on line 36

Warning: Cannot modify header information - headers already sent by (output started at /home/pwcakes/public_html/wp-content/plugins/appointments/includes/class.gcal.php:36) in /home/pwcakes/public_html/wp-includes/option.php on line 568

Warning: Cannot modify header information - headers already sent by (output started at /home/pwcakes/public_html/wp-content/plugins/appointments/includes/class.gcal.php:36) in /home/pwcakes/public_html/wp-includes/option.php on line 569

FOOTER:
Warning: Unknown: open(/tmp/sess_fd45b1589e0d14d2adf35d327cbc8da6, O_RDWR) failed: Permission denied (13) in Unknown on line 0

Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/tmp) in Unknown on line 0

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Thanks