When you are using the Forms view of your TurboTax CD/Download, the CCA claim on the T776 is one form that will allow an override, and still be eligible for NetFile. You cannot override Line 9936 itself, you must make your override in Area A - Column 12 for each Class of depreciable asset.
Make sure you return to Line 9936 and remove the override from there, and you should have no "Error" message preventing you from NetFiling. Screenshot attached.