Use the license file you received from Zimbra to generate a new activation file. To do that, upload the license file to the Zimbra server using a utility like WinSCP and enter:
su - zimbra zmlicense -i /path/to/license/file
Get the information required for the manual activation from the console at "Global Settings->License->Manually Activate License" (fingerprint, activation ID, license ID and version)
Go to support.zimbra.com and log in, go to the license page (use Internet Explorer). Enter the information and download the .xml file.
upload the .xml file and enter:
zmlicense -A /path/to/activation/file
Check for successful activation with