Visual Studio Not Implemented Error Fsharp Project

Feb 10th, 2017 - written by Kimserey with .

Yesterday I had an error prompting me the following error when trying to reference a project within my solution.

The problem was that I was referencing another project which was unloaded. When expanding the list of references, there is a warning sign for problematic references:

Most of the time, for me at least, it indicates a mismatch of F# version between the two libraries. But a mismatch of F# version doesn’t cause the not implemented exception on Visual Studio. The issue was that the library referenced was unloaded.

Once I made sure it was loaded, the sign disappeared and VS allowed me to add a reference.