This error happens when you've requested to connect to a computer but the request wasn't accepted. When someone requests to join, the host should see a Windows notification and a section in the interface. They can accept the connection via the interface or by pressing CTRL+F1.
The Windows notification might not show up if it's disabled or in Focus Assist mode. In that case, just accept via Parsec's interface.
If you're using the same account as the host PC to connect to your own machine, that PC may have crashed. Check if Parsec is running on it or restart the host PC if it's a cloud machine. If you still have issues let us know on Discord.