QCS installation log file "Upgrader.log" can be found by default under "C:\Program Files\Quest Software\Collaboration Services\ACSLOGS\Debug". However since the error code pertains to the windows installer process, this log may not contain enough information. In order to troubleshoot this error, installation needs to be executed with an option to create setup log file. This can be done in two ways:
1. Execute installer command to install QCS msi package (placed by default into Upgrader folder) with the switch that enables logging, for example:
msiexec.exe /qn /i "C:\Program Files\Quest Software\Collaboration Services\Upgrader\QCS.2.0.246.00.msi" ACSCOPYFILES="YES" /l* log.txt
2. Turn on Windows installer logging via modification of registry key below:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Installer - "Logging"="iwearucmopv!"
Installer log file will be saved in the %TEMP% folder on the console. The produced log file will contain more information on why the setup failed.