Another version of this software already installed ...

When installing MSSQL server 2005 Express edition, if you encountered this error while running the setup.exe 'Another version of this software already installed ..', when in fact you have removed previous failed installation. This will help you.

This problem is actually due to extraction of the installation package, which is a zip file. If you click on the installation package(which is an exe directly), Windows will make use of default compression software (winzip,Winrar and etc) to extract the package into a temp folder.

However, the problem is that sometimes the extraction goes wrong and thus it creates the problem of 'Microsoft SQL Server Native Client cannot be found' and 'Problem installing SQL Server 2005 fails on MSXML6'. Check out here.

This is probably because the file wasn't extracted properly or the default compression software is not compatible with the format. This can be proven when you try to use the default software to extract the file into a location manually and then if you try to run setup.exe, it will give you the message 'Another version of this software already installed. ....' If you would take note, the corrupted extracted file structure is different from the valid file structure.

To solve this problem, first of all, remove all fully installed or partially component from Control-Panel/Add or remove program (including MSXML 6.0 parser). Make use of the cleanup utility to make sure that all 'dirt' are removed. For instance, if after having removed MSXML 6.0 parser from control panel and you still find it under cleanup utility, then you must remove it too. Then use a proper compression software like Winzip or Winrar (don't use IZArc for this purpose) to extract the installation package into a designated folder and run setup.exe.

I can pretty sure that there will be no more problem. Take note that under XP home basic SP2, there is another window updates called MSXML 4.0 parser (6.10.1200.0) (KB933579) which may create confusion for you, but you don't have to uninstall it in order to get MSSQL 2005 express edition to install properly. (The MSXML 6.0 component would be installed without problem)