The error it's caused by another defective installer of another product, which has mistakenly changed the file encoding, without changing the XML header accordingly so, in your case, one of the file was encoded as UTF-8 and the other was encoded in UTF-8 with a BOM mark, but both XML headers still indicated the Windows 1252, which is the default for FSX.
This, of course, resulted in an illegal XML file, since the header doesn't match the actual encoding of the file and, since our installers correctly ask to Windows if the XML file is legal BEFORE trying to change it (if it didn't, the file would be easily corrupted even more), when a corrupted XML file is found, you are issued with the error, so the installation will not continue until you fix the errors.
There has been reports that an old version of Active Sky caused this corruption, but it was fixed later releases.
As discussed in all other threads related to this error, the solution is to open the files with a text editor that allows you to change the file encoding and save it back. The free Notepad++ program can do this: download it, open the files, than save them back using
ANSI encodinghttps://notepad-plus-plus.org/
