Note: The following message was originally posted by an unknown forum member on 03/20/2010, but was flagged as spam. I'm manually reposting it here to make it available to everyone.
[First a hearty thank-you for this amazing utility. It is indispensible. Much, much thanks to you for your generosity in making it available to others.]
I discovered this problem with .msu files when I was trying to install Microsoft Virtual PC. I went to the Virtual PC homepage, downloaded Windows6.1-KB958559-x64.msu, clicked on it, and Microsoft Word tried to open it. When I uninstalled Word, and tried again, another incorrect program tried to open the file (HTML-Kit.exe). So, the assocation of .msu extension with the wusa.exe, the Windows Updater stand alone executable, had been altered somehow. I did allow changes to file associations during installation of uniextractor, so I presumed this was the source of the change to .msu files in my case.
This is just a note to inquire whether installation of uniextractor alters .msu file associations such that clicking on those files no longer launches Windows updater program (wusa.exe) to install them. I don't know for certain, but it seems likely to have been the cause in my case, so I thought I'd post this query here.
Note that to fix this problem behavior for .msu files, you simply resore its association with the Windows utility, "wuse.exe", located somewhere in your Windows folder. In my case the correct folder was \Windows\SysWOW64\wusa.exe. I'm not sure where this file is located in other versions of Windows, but you can always locate it before doing the steps below, by searching for "wusa.exe" in the Windows search box.
1) Right-click on top of any .msu file (for example, the Virtual PC .msu file downloaded from Microsoft--search google for the Microsoft link to the "Virtual PC" or "XP Mode" homepage)
2) Choose "OPEN WITH..."
3) In the navigation box that pops up, make sure the "Always Open with" checkbox is CHECKED
4) If 64-bit Windows if your operating system, navigate to Windows\SysWOW64\wusa.exe. Select that, and click OPEN in the navigation box's bottom right corner.
"wusa.exe" stands for Windows-Updater-Stand-Alone executable.