The Override forecast line item won't accept the formula?
What am I doing wrong?
You are not supposed to write any formula in that line. It is supposed to be Input Line. However you may have to apply DCA to that line which we do in Blue print mode of the module in Read and Write Access Drivers.
Hope that helps
If you want to apply dca to override forecast line item , then it should be an input line item with dca ( in blueprint ) based on boolean like override , so for example when override is checked , then forecast can be entered(write based on true value of override) else it will be locked