Okay this means that the device you’re connected to doesn’t support bit-level writes on registers via the MaskWriteRegister function.
You’re going to have to use a derived tag or scripting function that reads, masks, and writes a new word back down instead. There’s an old post discussing the derived tag setup here: Troubles making a Derived Boolean Tag work as a mask for a Short Tag and there’s probably multiple posts discussing the scripting approach floating around.