Issue
The ACS emulator does not interact correctly with the Close Emulator action like it does with other emulators.
Error Code
Invalid Target error
Resolution
A work around is using the PowerShell action and running the following commands.
The PowerShell action is listed under Advanced in the Actions menu on the left side of the bot
In the section that says "Code" type the following commands:
$process = get-process acslaunch_win-32
$process.closemainwindow()

When it closes, the emulator sends a "save as" message, even if the "Save to" checkbox is not checked.
It is easier to target the box, send a tab keystroke to move the option to "No" and then target it again and send a click so that it doesn't save.
This will close the window without locking the session.
Additional Information
If this doesn't work, check the process name by going to the properties of the emulator and copying the name. Do not include .exe at the end of the process name.
This is where the Process name is:

Sample Botflow:

Related Links
In this link below, at the bottom, there are step by step instructions on how to set up the IBM iAccess Emulator to work with Nintex RPA.