Update error: "Could not open file to write"

[Fauxglove Silverweb]

Received error while updating: Error opening file for writing: c:\programfiles(x86)\SecondLifeViewer\Winmm.dll

Uninstalled and reinstalled  as recommended in similar answered question, identical error occurred

Worked around by removing the offending files from the target folder as errors were encountered and selecting "Retry".

Full list of affected files:
libeay 32.dll
msvcp100.dll
msvcr100.dll
msvcr120.dll
slplugin.exe
ssleay32.dll
winmm.dll

Is there a suggestion for preventing this from happening in the future?

Update: Having moved the files to a new folder and attempted to delete them, they all say they're being used by slplugin.exe.  Task manager can't force the program to shut down.

[Innula Zenovka]

I had that problem when I tried to update the viewer this time, too.

I resolved it by manually uninstalling the previous viewer, and choosing to allow the uninstaller to remove all items from the Second Life folder but telling it to keep other SL-related files (which include my chat and IM logs, and my settings) and then downloading the viewer manually and installing it.

That worked.