[Plugin: postTabs] Error on plugin activation

Hi and thanks for the great plugin!
I have WordPress 2.8.4 and when trying to activate the plugin, I keep getting the following error:

Fatal error: Cannot redeclare posttabs_init() (previously declared in /home/ronronmx/public_html/blog/wp-content/plugins/posttabs/postTabs.php:19) in /home/ronronmx/public_html/blog/wp-content/plugins/posttabs/postTabs.php on line 38

But, if I activate the plugin on a post per post basis (using Headspace 2), it works fine on the post where it’s been activated (in order to activate a plugin with HeadSpace 2, it has to be deactivated in the main plugins page).

Any idea why it won’t let me activate it normally?
Thanks!

http://ww.wp.xz.cn/extend/plugins/posttabs/