I’m thinking that you are performing the “Transmit” key in the Send Control Key activity. If it throws an exception when trying to use this key, then it’s possible that the Emulator is not supported that well by UiPath. In that case, you would need to code your emulation to use the Send Hotkey for some control keys, and have a selector string stored in a variable so you can reuse this; it will also be beneficial to ensure there’s only one emulation instance at a time so the selector can be easier to use.
FYI, I’m in the same situation in my company where we switched to TTWin Emulator, and many of the control keys don’t work. But, I coded it with some Send Hotkeys and works really well, as long as you have some good logic to attach to existing connections and close out of existing instances when the connection does not exist yet.
EDIT: “Transmit” is normally same as Enter key