Ryan’s Theme-switcher plugin not working!

I am thoroughly depressed. The themeswitcher plugin is not working for me from: https://dev.wp-plugins.org/wiki/ThemeSwitcher

I’ve downloaded the file, uploaded it into the plugins directory, and activated it the admin panel. But after activation, I got these errors at the very top:

“
Warning: Cannot modify header information – headers already sent by (output started at /home/snet/public_html/wp-content/plugins/theme-switcher.php:2) in /home/snet/public_html/wp-admin/admin.php on line 10

Warning: Cannot modify header information – headers already sent by (output started at /home/snet/public_html/wp-content/plugins/theme-switcher.php:2) in /home/snet/public_html/wp-admin/admin.php on line 11

Warning: Cannot modify header information – headers already sent by (output started at /home/snet/public_html/wp-content/plugins/theme-switcher.php:2) in /home/snet/public_html/wp-admin/admin.php on line 12

Warning: Cannot modify header information – headers already sent by (output started at /home/snet/public_html/wp-content/plugins/theme-switcher.php:2) in /home/snet/public_html/wp-admin/admin.php on line 13″

But the rest of the admin panel displays okay.

I inserted the needed code in sidebar.php, and tried choosing a different theme. The theme did NOT change, and I got the following errors at the top of the page:

“
Warning: Cannot modify header information – headers already sent by (output started at /home/snet/public_html/wp-content/plugins/theme-switcher.php:2) in /home/snet/public_html/wp-content/plugins/theme-switcher.php on line 38

Warning: Cannot modify header information – headers already sent by (output started at /home/snet/public_html/wp-content/plugins/theme-switcher.php:2) in /home/snet/public_html/wp-content/plugins/theme-switcher.php on line 45″

They all seem to do with “headers already being sent out.”

If I deactivate the plugin, everything goes back to normal (no php errors).

Another thing I’ve noticed is that when I deactivated the plugin, all of my other plugins also got deactivated. I hope that’ll stop when I fix the main problem.

Please help me, I will give you imaginary chocolate chip cookies ??