Error: session_start() - Started after domain mapped

I receive the following error after migrating my site and mapping the domain. The subdomain site didn't have this problem:

Warning: session_start(): open(/tmp/sess_100447e98d2021efb38e2b5f110007d1, O_RDWR) failed: Permission denied (13) in /home/newly_mapped_domain/public_html/wp-content/plugins/custom-sidebars/inc/external/wpmu-lib/inc/class-thelib.php on line 114

I do not get this error on my other mapped domains for this multisite, and they are all using the same plugins with virtually the same code.