According to this:
This record of Windows Installer error codes on MSDN lists 1605
incorrectly as an indicator for not enough free space available on the
target drive; DesktopEngineer.com however, states that 1605 designates
a missing product, required to complete a custom action successfully:
1605 ERROR_UNKNOWN_PRODUCT This action is only valid for products that
are currently installed.
The solution that the link provides is this.
Trial and error to the rescue.
So by means of elimination,> the following simple solution appears to be fairly effective.
Delete the registry key’s parent containing 56A968A049C8C7F45A7C79D2C3C8DEE9
In this particular case, deleting the 7AB711B11CB5E91428E0D7F4F314C2B7 key first (GUID transformation), results
in a successful installation of SQL Server 2008 R2 afterwards:
Microsoft often moves in mysterious ways.
How to transform the GUID very simply?
- Run Registry Editor (type regedit in Start Search or Run dialog box and press enter) and navigate to-
- Take the first part of GUID and reverse it, in my case it is AA4A4B2C and its reverse string is C2B4A4AA. Now search for C2B4A4AA
and you’ll get a match than delete the its parent subkey (it will be a
kind of GUID without braces).
- Now run the Setup again, it will go smoothly without any hassle.
See this link about the solution