There are 2 locations to uncheck the K-1 Line 16 box (that indicates an attached K-3). The first is in the TT software as you go through line-by-line. This is where sometimes it will not allow you to uncheck it.
The second location is in "Check this Entry". Access this by running "Smart Check". If you have Box 16 checked, but have zeros or blank cells (because all income/tax is U.S.-based) it will return an error, and launch "Check This Entry." In that screen there is a "Box 16 checkbox" shown. You can uncheck it here. Then hit "Continue" at the bottom.
