Hello there!
First of all. I recommend you to deactivate ALL you current active plugins on your WordPress installation, and switch to a default WordPress theme like Twentyseventeen using FTP or cPanel files manager, and check if the problem is gone.
If so, the definitely the problem is caused by a plugin or you theme. Activate them one by one until you find what one is causing this mistake.
Let me know if this helps you with this issue.
Errors like this are logged. Check the error log on your server. If you can’t find the log, please contact your host.
Meantime, enable wp_debug and wp_debug_log and after an error, look at wp-content/debug.log to see if anything gets logged there. https://codex.wordpress.org/Debugging_in_WordPress
You can also try this: Please attempt to disable all plugins, and use one of the default (Twenty*) themes. If the problem goes away, enable them one by one to identify the source of your troubles.
If you cannot access wp-admin, there are other ways to deactivate plugins.
okay i managed to get this fixed by deleting the theme and plugin
