By “activate” I mean activating the plugin, slp4-tagalong.zip
By environment, maybe you mean WordPress version 4.2.4
Store Locator Plus from store-locator-le.4.2.67.zip
After uninstalling all SLP related plugins, and then cleaning out all SLP related entries in the wp_options table (because the SLP doesn’t work for some reason), and dropping the wp_store_locator table, I was able to reinstall all plugins and get everything to work.
Please consider this case solved.