Not sure what this issue is:

[MrAnime-0001]

Framework: .NET 8.0.2
RuntimeIdentifier: win-x64
OS: Microsoft Windows 10.0.26200

No mkv file info.

System.IO.IOException: The process cannot access the file 'C:\Users\Yutti Chylong\Downloads\I Left My A-Rank Party to Help My Former Students Reach the Dungeon Depths!\I Left My A-Rank Party to Help My Former Students Reach the Dungeon Depths! S01\Aparida S01 E21.mkv' because it is being used by another process.
at Microsoft.Win32.SafeHandles.SafeFileHandle.CreateFile(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options)
at Microsoft.Win32.SafeHandles.SafeFileHandle.Open(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, Nullable1 unixCreateMode) at System.IO.Strategies.OSFileStreamStrategy..ctor(String path, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, Nullable1 unixCreateMode)
at System.IO.Strategies.FileStreamHelpers.ChooseStrategyCore(String path, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize, Nullable`1 unixCreateMode)
at System.IO.File.Open(String path, FileMode mode)
at MatroskaLib.MatroskaReader.ReadMkvFiles(String[] filePaths)
at MatroskaLib.MkvFilesContainer..ctor(String[] filePaths)
at MkvDefaultTrackChanger.MainForm.LoadFiles()
at MkvDefaultTrackChanger.MainForm.BtnBrowseFilesClick(Object sender, EventArgs e)

[MikeMoolenaar]

The mkv file is being user by another program. For example, It may be open in a video player.

I should probably make the error message more clear...