Gravity forms 2.5.2 - Critical Error on submission

On form submission the error as below comes up:
There has been a critical error on this website.

This was not any issue before but recently has come up.
Pls advise what could be wrong and what troubleshooting can be done to make this work.

thank you

Please contact your web host and ask them to check the site error logs for the error details.

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