At a deployment where the NetBackup 6.5 is installed on the Windows 2003 primary server, the NetBackup 6.5.5 installation package was successfully installed. However, the NetBackup version shown in the NetBackup management interface was still 6.5. The upgrade failed.
A NetBackup upgrade compares the system time and the file time. If the resulted time skew on the server is major, replacement of some files fails, causing an upgrade failure.