This is just going to be a really quick post on how to solve this problem I get occasionally and it fits in with what was made in the post on using MonoGame with F# interactive. When you try and compile an F# project, you may get a series of warnings telling you that the file copy operation timed out. Then after 10 of these warnings you get an error and a build failure. This error probably means that the library you are trying to use was referenced in the F# interactive window by using the #r directive.
To solve it you have to simply reset your interactive session by right clicking within the F# interactive window and selecting reset interactive session. Unfortunately there doesn’t appear to be a way of dynamically unloading any assemblies and so you will end up losing your current interactive session.