FP1 is Feature Pack 1 for BE 15. You should download the one with FP1 and use that that.
There are 3 ways to get FP1
1) Complete installer with FP1 already applied (from trailware or file connect) - this is used to install a brand new server or to upgrade from BE 2014, 2012 or 2010 R3, BUT is not for 2015 original release to FP1
2) LiveUpdate - only used where BE 15 original release is already installed
3) from the technote posted by VJware - only used where BE 15 original release is already installed and either because of no direct internet access or because of a failure LiveUpdate installs.
With regards your issue, in some instances liveupdate will fail if your server is resource challenged and the Backup Exec services do not stop quickly enough - fix for the can be get liveupdate started and before you actually click to start the download and install, stop the Backup Exec services manually first.
There is however a second reason why LiveUpdate fails - sometimes the original install media needs to be available for the patches to succeed. Unfortunately the live update mechanism cannot pop-up the dialog box asking you to confirm where the install media is so you get a failure. The manual download (option 3) should correct this (and might even correct it without needing the dialog pop-up, if the install files are available in the original path.
Finally in a CASO environment you may have to disable communication to the managed media server(s) before liveupdate will let you update the CAS server (which you also need to do before upgrading managed servers)
