I was testing something that I never do (something that probably no one has much reason to do) in order to answer a question and got the error.
Steps to reproduce:
1. Select two files that do not have the same artwork (embedded or linked)
2. Right-click -> Edit
3. Artwork Tab
4. Attempt to deselect "primary picture"
Error:
MusicBee v3.3.7410.35016D (Win10.0), 15 Apr 2020 7:55:
System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
at #=zSb0$dnNrm0verrFMQqDMA2c=.#=zXiL4dW9s13_I1h$Asg==(Object #=zqTfSmUM=, EventArgs #=znysUjIk=)
at System.Windows.Forms.Control.OnClick(EventArgs e)
at #=z_n$YUYxNWFK0JeRTPJ81RDw7dtLZ.OnClick(EventArgs #=znysUjIk=)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)