I had a similar issue that I manged to fix by doing the following; not sure if it will work for you:
a) Remove all Hamachi references in registry (using F3 to search)
b) Create a new user account on your Windows 7 computer
c) Logon as that new user, install Hamachi 2 and restart
d) Logon as new user, test to see if it works, - if so, restart, logon as original account and delete the new user account.
[8F] The NyQuil Kid