Plugin Error / Can't Access Dashboard

I have received the following warnings when I try to visit my site and acces my dashboard:

Warning: session_start(): open(/tmp/sess_f485a7f817780dbf976f03bbaca10c46, O_RDWR) failed: No such file or directory (2) in /home/jfalbe/public_html/wp-content/plugins/custom-sidebars/inc/external/wpmu-lib/functions-wpmulib.php on line 69

Warning: session_start(): Cannot send session cookie – headers already sent by (output started at /home/jfalbe/public_html/wp-content/plugins/custom-sidebars/inc/external/wpmu-lib/functions-wpmulib.php:69) in /home/jfalbe/public_html/wp-content/plugins/custom-sidebars/inc/external/wpmu-lib/functions-wpmulib.php on line 69

Warning: session_start(): Cannot send session cache limiter – headers already sent (output started at /home/jfalbe/public_html/wp-content/plugins/custom-sidebars/inc/external/wpmu-lib/functions-wpmulib.php:69) in /home/jfalbe/public_html/wp-content/plugins/custom-sidebars/inc/external/wpmu-lib/functions-wpmulib.php on line 69

Warning: Cannot modify header information – headers already sent by (output started at /home/jfalbe/public_html/wp-content/plugins/custom-sidebars/inc/external/wpmu-lib/functions-wpmulib.php:69) in /home/jfalbe/public_html/wp-includes/pluggable.php on line 1207

Warning: Unknown: open(/tmp/sess_f485a7f817780dbf976f03bbaca10c46, O_RDWR) failed: No such file or directory (2) 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

I’ve attempted to clear my cache, as suggested in previous threads, and this has not solved my problem. I’m unable to access my dashboard to deactivate this plug-in. Please let me know how I can fix this.

Thanks!