You should try another constructor. They are documented at MSDN.
This one looks like a bet:
FileStream Constructor (String, FileMode, FileAccess, FileShare)
MSDN Link
FileAccess
A constant that determines how the file can be accessed by the FileStream object. This gets the CanRead and CanWrite properties of the FileStream object. CanSeek is true if path specifies a disk file.
FileShare
A constant that determines how the file will be shared by processes.
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