Do these before reinstalling SP1:
A few more questions: How many MSI files have you tried that have returned this message? Are they from a particular vendor? Are any of them Microsoft files downloaded from their website? And are they supposed to be compatible with the 64-bit OS or Windows 7?
First, where are these packages being run from? Were they downloaded to your Desktop, are they on a disk, or are they in a system directory such as somewhere inside C:\Windows?
If they are inside a system directory, try copying them to your desktop or another folder you have full control of and running them from there.
Second, try running sfc /scannow from your command prompt to check for and repair any system files or registry issues.
Third, are they blocked? Right click on the .msi file and select properties. There will be a button near the bottom of the dialog Unblock. Click this and try running the files again.
Fourth, make sure that the folder you've got the files in have the appropriate permissions. Check the security settings for the folder these files are in and make sure that the user SYSTEM has full access. After all, the msiexec will run as SYSTEM and will need full control of the directory and all files inside it.
Trying re-installing Windows 7 sp1 to perform a "lite" operating system repair.
Download the package from the MS website, you'll probably need the one labeled windows6.1-KB976932-X64.exe.
If you already have the Service Pack installed, you'll want to uninstall it. Sometimes these packs don't have a "repair" or "reinstall" function. Instructions from the MS site for uninstalling.
After the uninstall is complete and you've rebooted, begin the installation of the package downloaded in step 1.