I've had two Windows 7 clients (on x86 and one x64) that have failed to upgrade and one Server 2012. I've upgraded a total of about 15, so this is an unusually high failure rate.
I advertise the update from within SEPM. I do a silent install and then prompt for reboot on the Win7 boxes, or just wait for reboot on the 2012 box. In each case, the install appears to finish successfully. SEPM shows that the machines need a reboot. Upon reboot, no SEP client appears to be on the machine. After another reboot, the old client is running again, but the machines fail at subsequent upgrade attempts.
The SIS_INST.LOG on all three machines show a similar error (see below). I can attached the entire log if needed, but it's about 10 Meg. Please note, the 2012 server is a GUP, so it has the same Feature Set as the Windows 7 machines.
2014-10-15T12:33:31.161Z INFO I SIS Executing action ( 3388 ) - RunCustomAction currentPosition: 2514620
2014-10-15T12:33:31.161Z INFO I SIS
2014-10-15T12:33:31.161Z INFO I SIS Running custom action specified by objectID: {EA17B4EE-5378-498D-A017-7F132D30BFF1}
2014-10-15T12:33:31.177Z DEBUG I SIS Creating transaction.
2014-10-15T12:33:31.177Z DEBUG I SIS Created transaction 0x00000011:0x00000398
2014-10-15T12:33:31.177Z DEBUG I SIS Committing transaction 0x00000011:0x00000398
2014-10-15T12:33:31.192Z DEBUG I SIS Creating transaction.
2014-10-15T12:33:31.192Z DEBUG I SIS Created transaction 0x00000012:0x00000398
2014-10-15T12:33:31.192Z INFO I SIS SISCustomActionKManager starting
2014-10-15T12:33:31.270Z WARN I SIS SISCustomActionKManager failed to process C:\ProgramData\Symantec\Symantec Endpoint Protection\12.1.5337.5000.105\Data\Config\cltdef.dat.bak
2014-10-15T12:33:31.270Z INFO I SIS cltdef.dat
2014-10-15T12:33:31.333Z INFO I SIS serdef.dat
2014-10-15T12:33:31.333Z ERROR I SIS SISCustomActionKManager failed to process C:\ProgramData\Symantec\Symantec Endpoint Protection\12.1.5337.5000.105\Data\Config\default.dat
2014-10-15T12:33:31.333Z INFO I SIS SISCustomActionKManager complete
2014-10-15T12:33:31.333Z ERROR I SIS Failed custom action Execute() method with error: 0x80004005
2014-10-15T12:33:31.333Z ERROR I SIS
2014-10-15T12:33:31.333Z ERROR I SIS Dumping action parameters from the script:
2014-10-15T12:33:31.333Z ERROR I SIS ObjectID=[{EA17B4EE-5378-498D-A017-7F132D30BFF1}]
2014-10-15T12:33:31.333Z ERROR I SIS OldPath=[C:\Program Files (x86)\Symantec\Symantec Endpoint Protection\]
2014-10-15T12:33:31.333Z ERROR I SIS OldVersion=[12.1.4013.4013]
2014-10-15T12:33:31.333Z ERROR I SIS NewPath=[C:\Program Files (x86)\Symantec\Symantec Endpoint Protection\12.1.5337.5000.105\]
2014-10-15T12:33:31.333Z ERROR I SIS OnFail=[rollbackExecution]
2014-10-15T12:33:31.333Z INFO I SIS ExecuteScript() - Successfully set failure event.
2014-10-15T12:33:31.333Z INFO I SIS ExecuteScript() returning ACTION_FAILED_WITH_ROLLBACK
2014-10-15T12:33:31.333Z INFO I SIS
2014-10-15T12:33:31.333Z INFO I SIS script completed with status: ACTION_FAILED_WITH_ROLLBACK
2014-10-15T12:33:31.333Z DEBUG I SIS Rolling back transaction 0x00000010:0x0000026C
2014-10-15T12:33:31.333Z DEBUG I SIS Creating transaction.
2014-10-15T12:33:31.333Z DEBUG I SIS Created transaction 0x00000013:0x0000026C
2014-10-15T12:33:31.333Z DEBUG r SIS Committing transaction 0x00000013:0x0000026C
2014-10-15T12:33:31.442Z DEBUG r SIS Creating transaction.
2014-10-15T12:33:31.442Z DEBUG r SIS Created transaction 0x00000014:0x0000026C
2014-10-15T12:33:31.442Z INFO r SIS TransitionToEnteringRollbackScript() - success