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Loading custom MIME mappings failed

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



Loading custom MIME mappings failed
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

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]

  • Guest
  • Sep 21 2017
  • Under review
  • Attach files
  • Guest commented
    27 Sep, 2017 04:50pm

    Thank you,

    the file does exist on this path, I can open this with notepad, it is not marked read-only. I do not have anything like Dropbox or OneDrive installed on this OS. 

  • Eric Lawrence commented
    23 Sep, 2017 06:03pm

    If you look in Windows Explorer, does this file exist? If you open it in Notepad, is it read? Do you have anything non-default, like Dropbox or OneDrive File System integration installed?