Summary:

Customer made a new quote and was trying to edit/delete them. When the opportunity was clicked, the error message appears: "An Unexpected event has occured"

There was a field included in the opportunity status box table that was not getting a value and was not needed.

Resolution:

1. Go to Administration -> Customisation -> Secondary entities -> Opportunity Progress -> Screens
2. Click on the opportunity Status Box link
3. In here you will find the field “Opportunity Progress: Tracking Note(oppo_progressnote)”
4. Remove this field and save changes.