Unable to launch Notepad++ after RDP reboot

I've been using Notepad++ Portable on a Windows server at work that I connect to via RDP. There were some issues with the server and they rebooted the machine without warning us, so Notepad++ Portable was running when the reboot occurred. Now, when I reconnect and try to run Notepad++ Portable, it get the error "Another instance of Notepad++ is already running. Please close other instances of Notepad++ before launching Notepad++ Portable."

There are no instances of Notepad++ running on the server; it's just been rebooted (and I've checked the processes tab of Task Manager to be sure). I've tried re-downloading Notepad++ Portable and running from the new download and I get the same message.