I was trying to change the Authentication Mode of one the External Content Types (BCS) to ‘BDC Identity’ through SharePoint Designer, when this error was thrown.
Solution
The solution was to set the revert to self option of the BCS service to true. To do that, run the following in the Management Shell.
$bcsServiceApp = Get-SPServiceApplication | where {$_ -match "Business Data Connectivity Service"}
$bcsServiceApp.RevertToSelfAllowed = $true;
$bcsServiceApp.Update();
Piyush K Singh 