searchFilter plugin gives error: cannot modify header information

Can you help me figure out why I’m getting the error since adding this plugin…

the filter by boat at the top of this page… select one and click search button produces the error.

http://x.sonwatersports.com/boats-for-sale/used/

how can I make this work?
(I just put the shortcode for the searchFilter at the top of the page.)

Hi there,

It sounds like you might be having an issue with a third party plugin or script. Regretfully, we cannot provide support for third party plugins or scripts as our support policy in the sidebar states due to the fact that there is simply no way to account for all of the potential variables at play when using another developer’s plugin or script. Because of this, any questions you have regarding setup, integration, or troubleshooting any piece of functionality that is not native to X will need to be directed to the original developer.

For the error which you are experiencing I did a Google Search which can be a start for your investigation and report of the case to the plugin developer.

Thank you for your understanding.