Pacman error: FILENAME exists in filesystem

Question

This comes up quite often, and since users are not using the excellent forum search function, it will be stickied.
error: could not prepare transaction
error: failed to commit transaction (conflicting files)
libname: /insert/file/name/here exists in filesystem
Errors occurred, no packages were upgraded.
Why this is happening: pacman has detected a file conflict, and by design, will not overwrite files for you. This is a design feature, not a flaw.
It is the user's responsibility to maintain their system, not the package manager's. (pacman -Qo may be invoked to query which package owns the file, if any.)
What can be done to solve this: The issue is usually trivial to solve. A safe way is to firstly check if another package owns the file (pacman -Qo <full file path>).  If the file is owned by another package file a bug report If the file is not owned by another package rename (or remove) the the file which 'exists in filesystem', and reissue the pacman -Syu command. If all goes well, the file may then be removed.
As always, there may be exceptions, so check the front page Arch news, Announcement lists, and optionally the forum and Mailing Lists for possible known issues.
pacman can also be forced to overwrite the files, if you know what you are doing. Please read this post for more information.

Answer 1

If that's what happens, then there's something wrong. Let's call it common sense . 200 files is quite a lot. I've never had a 'massive' update myself that gave that many duplicate files - I hope you took the time to read Misfit138's recommendations and acted upon them - and I hope you update regularly, but your wording suggests you don't. That in itself can cause things to break more easily.
Also - I recommend you open your own topic instead of hijacking a sticky for this. This isn't supposed to turn into a help topic.