c# - What's wrong when 'the requested operation cannot be performed on a file with a user-mapped section open?' -

I am developing an application that is reading and writing a certain file on disk (but synchronously) However, how large the file is, the more I receive the following IOException:

The requested operation can not be performed on a file that opens a user-mapped section.

is being done from:

  system. IO error .__ error Virus (System32.If., Int32 rights, Boolean useRights, fileshare share, Int32 BufferSize, FileOptions option, SECURITY_ATTRIBUTES secAttrs, string msgPath, Boolean bFromProxy) on System.IO.FileStream..ctor (string path, FileMode mode, using FileAccess , fileshare share, Int32 BufferSize, FileOptions option) SystemkIOkStreamWriterkCreateFile (string path System.IO.StreamWriter..ctor on System.IO.StreamWriter..ctor, boolean append) (string path, Boolean attached, encoding Encoding, int32 bufferSize (string path, boolean append, encoding encoding) on ​​System.IO.File.WriteAllText (string path, st Ring Co ntents, Encoding encoding) System.Windows.Forms.Control.OnClick (EventArgs e) at System.Windows.Forms.Button.OnClick (EventArgs e) at System.Windows.Forms.Button.OnMouseUp (MouseEventArgs mevent) system . In WindowskFormskControlkWmMouseUp (Message & amp; m) (message System.Windows.Forms.Button.WndProc & amp; m) (message System.Windows.Forms.ButtonBase.WndProc & amp; M , MouseButtons button, Int32 clicks System.Windows.Forms.Control.WndProc (message & amp); m) in System.Windows.Forms.NativeWindow.DebuggableCallback (IntPtr hWnd; System.Windows.Forms.Control.ControlNativeWindow. System.indo.form at WndProc (Message & amp; System.Windows.Forms.Control.ControlNativeWindow.OnMessage (Me on Message & Interpretation), Interpreted Media, Interpetrip Liparum). UNICEFANETNET Medips On Dispatches Messageway (MSG & MMS) systems. Windows .form. Applications. Comptant Manager System. Windows .form. UnisonFinitive Memoirs. Comptant Manager FUPM Message Loop (Int 32 Dv Component IDID, Int32 Cause System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner on Int32 pvLoopData) (Int32 Reasoning ApplicationContext Reference) System.Windows.Forms.Application.ThreadContext.RunMessageLoop (Int32 due to ApplicationContext reference) in S.Forms.Application.Run (Form mainForm) TestApp.Program.Main () on System.Window  

as you can see, with the exception of the File.WriteAllText < / Is removed from within the code>. I suspect that this exception was to be done together with reading and writing, so tried to limit access to the file. Instead of pausing them both a lock and a mutex seemed to increase the number of exceptions. So what's really going on? What exactly does this exception mean and how can it be stopped?