Error Deactivating, Deleting or Installing Plugins

I’ve encountered an issue today that I’ve never seen before. I have been trying to uninstall Ajax Event Calendar because it says that magic quotes is on my server… I have GoDaddy hosting and they say this is not the case. I tried all the fixes suggested in the plugin’s support forum and none of them worked so I simply decided to go with a different calendar, however, whenever I deactivate ANY of the plugins (because I saw a few junk ones in there that I don’t need) none of them are saving as deactivated and I get this message when I click to delete them:

Warning: Cannot modify header information – headers already sent by (output started at /home/content/17/9902817/html/wp-content/themes/magazino/functions.php:902) in /home/content/17/9902817/html/wp-includes/pluggable.php on line 1121

That seems to be something with my theme, right? This has never happened before, however, and I’m thoroughly confused and not sure what to do from here. When I tried to just skip the plugins and install a new one, it showed that it was successful but is not showing in my list of plugins now. I’m totally at a loss. The website, if it’s necessary for assistance, is blisstival.com.

Thank you in advance for any advice. ??