Query statements MUST return the ROWID to be updatable. For example:

select * from employee where salary > 2000

would not be updatable, whereas:

select employee.*, rowid from employee where salary > 2000

would be updatable.

To reduce this obvious nuisance, you can use the TOAD-specific EDIT statement. For example:

edit employee where salary > 2000

If the resultset should be editable but remains read-only, make sure the TOAD Options > Data Grids - Data tab, Default to Read-Only Queries checkbox is NOT enabled