I clicked on your site and I didnt see anything broken.
Could you provide the exact page that is broken that you are using Store locator plus on?
We also need Your Plugin environment which will indicate versions, add-ons and version of WordPress(see under your Plugins click on SLP, click on INFO)
It appears based on that error message you may have been using an older version of Word press that at the moment is not compatible with the version of Store locator Plus, but I cant be sure without more information.