Recieving error: Fatal error: Class 'panels_renderer_standard' not found in
Check your modules/panels/plugins/display_renderers folder and make sure there is a file named panels_renderer_standard.class.php inside, that's where the class is contained that is supposedly missing.

Try completely replacing the panels module code with a fresh download, that is: move the current module folder somewhere else (so you can get it again if you need to) and re-upload the module.

If you're applying any patches, make sure you check them for code that might be deleting, renaming, or disabling the display_renderer_standard class.