Unfortunately, there is no way for Shopp to know and report which plugin is actually causing the error. To determine which active plugin is causing the problem you will need to selectively deactivate plugins, one at a time and reload one of the Shopp admin pages with the notice to see if the notice goes away. The best approach is the following:
- Load a Shopp admin page with the notice in your browser
- Open a new browser tab (or new window) with your WordPress Admin → Plugins → Installed screen
- Deactivate a plugin, switch to your Shopp admin page tab (or window) and reload it
- If the error notice disappears, you’ve found the offending plugin – note the name and version and add it to the Shopp Compatibility List.
- If you want to be really nice: reactivate the bad plugin, grab the errors out of your browser’s error console and report them to the plugin author so they can fix it in their next release