This can happen if another program corrupts your Hamachi configuration or identity information.

To fix whatever corrupted your configuration,

1. Click Start, then Run.
2. Type %APPDATA% [hit Enter]
3. Rename the Hamachi folder.

The next time you start Hamachi, it will connect as if for the first time, but the issue should be resolved. Note that me> refers to the Windows username that Hamachi was installed with.