Error "Concurrency violation" when trying to update data. (4226530)

I am getting the error "Concurrency violation. Expected to update 1 row(s), but actually updated 0 row(s)." when I try to insert, update, edit or delete any data from any table.

RESOLUTION 1:
Please try the following option:
1. Go Tools | Options | Environment |Grid and uncheck the option "Show data as read only"
2. Click on the Apply and OK button.
3. Exit Toad
4. Load back into Toad to retest.

RESOLUTION 2:
1. Select Define window via the down arrow icon of the Green circle icon of Data Grid
2. Ensure to check all primary key columns under KEY COLUMNS field