From the Bank Accounts page I selected the Modify button which opens the “Modify Bank Account” page
so I could tick the box "Show bank account summary on the dashboard"
After saving it I could not longer access the Chart of Accounts
I remembered when this happened before (when changing the spelling of my banks name) so I checked my journals and found that the system had auto created an extra journal entry on the original opening bank balance journal.
The extra entry was to the “Suspense Account” unbalancing that journal so the chart of accounts and balance sheet became unavailable
Deleting that extra journal entry corrects the problem but its a bug that needs addressing.