You have it open already from not exiting properly...you need to close it before you can open it again....
Go to your USERS file and open your file..... then APPDATA then LOCAL then TEMP
With SM off there should be no slices showing so delete any that are and reboot SM and you will be ok
You will probably see a WSJT-X Slice 1 or 2 or an AB depending on what you called them but with SM closed there should not be any so delete any that show ... always close SM first and let it close the slice windiws
Is there any chance you have DAX Control Panel running on another computer? In the DAX Control Panel hover the mouse over the button for your IQ Stream 2. You should get a pop-up telling you the IP address of the other computer... if that's what's going on.
EDIT: ...sorry, it wont tell you the IP address of the other computer, but it will tell you that it's in use by another computer.