As the error suggests, it is a problem related to thank me later WordPress Plugin. I guess, you have updated the Thank Me Later plugin and since the problem occurs.
For the time being, you need to deactivate this plugin and I guess you are not able to login to your dashboard also. So, login to your CPanel first and go to wp-content/plugins page and compress the Thank me later plugin files. After this, delete the original Thank me later file.
Now try to go to your website/wp-admin/plugins page. It will open now. Go to cpanel again and extract the compressed Thankmelater plugin files and delete the compressed one. Now refresh the Wordpress admin/plugins dashboard. You will find your Thank me later plugin but it wil be deactivated.
Don't activate it now, wait for the next update from the plugin author.