[c#] Access to the path denied error in C#

tl;dr version: Make sure you are not trying to open a file marked in the file system as Read-Only in Read/Write mode.

I have come across this error in my travels trying to read in an XML file. I have found that in some circumstances (detailed below) this error would be generated for a file even though the path and file name are correct.

File details:

  • The path and file name are valid, the file exists
  • Both the service account and the logged in user have Full Control permissions to the file and the full path
  • The file is marked as Read-Only
  • It is running on Windows Server 2008 R2
  • The path to the file was using local drive letters, not UNC path

When trying to read the file programmatically, the following behavior was observed while running the exact same code:

  • When running as the logged in user, the file is read with no error
  • When running as the service account, trying to read the file generates the Access Is Denied error with no details

In order to fix this, I had to change the method call from the default (Opening as RW) to opening the file as RO. Once I made that one change, it stopped throwing an error.