Error while upgrading to v14

Hi All,
I am trying to upgrade v13 instance to v14. Also have 1 custom app, but it gives some error and site is down. Please find the attached screenshot for reference.

Trying to resolve this from long time. It would be helpful if I could get some help or suggestions on this.

Thanks

Hi,

It may help to say the operating environment, and the steps taken to attempt the upgrade.