The system environment check returned errors. Those errors will affect the functionality and stability of your TYPO3 CMS instance. Please check the install tool "System environment" for all details.
The first image shows the typo3 backend status report error:
Here is the error on browser when I tried to access the frontend of the website:
About the exception you are getting: It seems you stumbled upon a bug which is fixed in latest version 7.6.26. Please update to the latest version. Make sure you follow the correct procedure for updating.
If the problem still occurs, clear the system cache in the install tool.
More general hints:
#announcements
in the typo3 slack workspace. That way you will be notified as soon as a new TYPO3 version is released. If you don't have access to the TYPO3 slack workspace yet, register for an invite.