Just before the update, no issue, after the update, this occurred. Verified on other machines as well.

File permissions are read, write, execute, to root of the drive

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Loading custom MIME mappings failed
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Fiddler has encountered an unexpected problem. If you believe this is a bug in Fiddler, please copy this message by hitting CTRL+C, and submit a bug report at http://www.telerik.com/forums/fiddler.

Access to the path 'D:\Users\josh\Documents\Fiddler2\CustomMimeMappings.xml' is denied.

Type: System.UnauthorizedAccessException
Source: mscorlib
at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)

at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)

at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, String msgPath, Boolean bFromProxy)

at System.IO.FileStream..ctor(String path, FileMode mode)

at Fiddler.XmlFileMimeMappings..ctor(String filePath) in C:\JenkinsHome\jobs\FiddlerReleaseBuild\workspace\Fiddler2\Common\Core\MimeMapping\XmlFileMimeMappings.cs:line 38

at Fiddler.frmViewer.?(Object , EventArgs ) in C:\JenkinsHome\jobs\FiddlerReleaseBuild\workspace\Fiddler2\Viewer.cs:line 9816


Fiddler v4.6.20173.38786 (x64 AMD64) [.NET 4.0.30319.42000 on Microsoft Windows NT 6.1.7601 Service Pack 1]
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OK
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