I am running the latest (9.04).version and I am getting this message. when trying to open an older schematic file?
Error loading schematic. : Kicad was unable to open the file because it was created with a more recent version than the one you are running.
When I look at the version under error, it shows Kicak 8.08?
I thought that previous versions were removed or overwritten?
Can you post Help/About KiCad/Copy Version info. Need the OS you are running on.
Also fix the version to 9.0.4 / 8.0.8 so data won’t mess up future search results (There is no .04 or .08)
On Windows you can have V8 as well as V9 on the same machine. It looks like you have run a V8 version
Edited your title to be more informative for future searches.
That’s possible at least if some shortcut points to the older kicad, or file suffix assignment has been kept and you double click on a file. Open KiCad, make sure it’s v9 and open the project. You can safely uninstall v8 if you don’t need it.
Running WIN10 Kicad ver 9.0.4
The odd thing is, some files it asks to save in ver9, others it just says cannot load, older version, another oddity, some of these files were recently produced under a ver of 9??
Are you certain ? or maybe the Nightlies ? the Nightlies are a newer version and often files saved under the Nightlies cannot be opened in the currently released version.
Post a sample project here and we can see what version it is.
Instead of trying to figure out what is actually happening, isn’t it simpler to just uninstall / remove all traces of KiCad and do a fresh install?
Also: Where did you get the installation files for KiCad? Is it from some official location, or did you get them from some shady untrusted source?
If you open the *.kicad_pcb file & *.kicad_sch file in a text editor and post the first 10 lines here, maybe others will be able to understand the situation.
ps.
If could see the “generator_version” in the warning, might be able to avoid the same problem. 
Another oddity, I ensure I am running 9.0.4 and I save the file OK, when I look at the entry using search it has added Kicad schematic 8 on the end?
If I remove ver 9 and re install it I assume the my recent files will remain?
BTW I went to the official site to download ver 9.0.4
ALWAYS make backups. Your project files and personal libraries should be outside the program directory, but, let us not ass u me that. 
Maybe you just haven’t changed the default application for each file extension in Windows File Explorer? I think that’s not a problem with the KiCAD application, but rather a problem with the user and the OS not being familiar with how to use the functions.
For more information, please search for and read Microsoft’s documentation on how to use Windows File Explorer.
To change the default application for a file type in Windows, right-click the file in File Explorer, select “Open with” > “Choose another app,” and then check “Always use this app to open .[file extension]” before clicking OK. Alternatively, open the Start Menu, search for and select “Default apps” to open the settings, find the desired file type, and choose your preferred application from the list.
You Can open this file in a text editor, paste the first 10 lines of the file here, and publish it.
By the way, opening files with this extension (.kicad_sch) from File Explorer can be confusing, so you’ll likely be happier if you always start working by opening the project file (*.kicad_pro).
You need to get used to point 3 above.
memo:
Windows : %APPDATA%\kicad\9.0
This is because you set KiCad8 as the default tool for kicad_sch files. You can change that to KiCad 9
So, you want to re-install v9 to choose it as the default file handler for kicad files. In that case you can just run the installer again, choosing the checkbox in the installation wizard when it appears.
The installer or uninstaller doesn’t delete your documents.
You can of course change the file associations in Windows configuration, too.
The essence of the problem in this thread must be due to the user’s ignorance of the version used when the file was last edited and the installation path of the application that starts by default with the Windows extension after installing two versions. Therefore, it is important to individually list and publish the KiCAD version information written at the top of the schematic or assembly diagram to be edited.
You Can open this file in a text editor, paste the first 10 lines of the file here, and publish it.
The file you are trying to edit has already been edited at version number (x). The application version is (y). You cannot edit an older version than the version that has already been edited. Perhaps a message like this should be displayed to warn the user of the two version numbers.
Yes, but also windows. At some point I had the default program for kicad_pro set to KiCad9 and for kicad_schem it was the KiCad8 schematic editor. This is very confusing to someone that doesn’t know that windows handles it that way.
Especially if the type field is abbreviated:
I cannot find any vestige of previous Kicad to ver 9 When running an older .pro file I get this:
