Session Cache Limiter and Session Cookie Warnings

(For those who have been following the cascade of error messages, the memory problem seems to be solved at this point. This error appears to be unrelated.)

I have two major errors that are showing above the nav bar on my HOME page only. These errors do NOT occur on ANY other theme I have tested (I've tested almost 40). And it does not occur when ProSites is deactivated. However, I had both Thesis and ProSites working together without the error for about two weeks. (The warning began to show up soon after I installed the new "Events" plugin, but didn't go away when I deactivated it.)

The only plugins running at this time are:
Thesis Openhook (at the site level)
ProSites (at the network level)

This error shows in ALL browsers:
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/popcred/public_html/wp-content/themes/thesis_182/lib/html/frameworks.php:6) in /home/mysite/public_html/wp-content/plugins/pro-sites/pro-sites.php on line 639

This error shows only on my iPad and iPhone:
Warning: session_start() [function.session-start]: Cannot send session cookie - already sent (output started at /home/sitename/public_html/wp-content/themes/thesis_182/lib/html/frameworks.php:6) in /home/sitename/public_html/wp-content/plugins/pro-sites/pro-sites.php on line 639

Thanks for any help.