Mutual recursive types are not defined when using lists inside

I'm having a problem compiling an old F# project located here. Offending file is here.

It uses mutual recursive types and it's correctly defined indentation-wise. But none the less, not EDNValue nor EDNValueParsed are seen at the same context/indentation level.

module EDNParserTypes =
 type EDNException(message : string) = 
    inherit System.Exception(message)

 type QualifiedSymbol = 
    struct
        val prefix: string
        val name: string
        new (prefix, name) = {prefix = prefix; name = name}
        override this.ToString() = "QualifiedSymbol Prefix: " + this.prefix + " Name: " + this.name 
    end

 type EDNValue = EDNNil
                | EDNBoolean of bool
                | EDNString of string
                | EDNCharacter of char
                | EDNSymbol of QualifiedSymbol
                | EDNKeyword of QualifiedSymbol
                | EDNInteger of BigInteger
                | EDNFloat of double
                | EDNComment of string
                | EDNDiscard of EDNValueParsed
                | EDNTaggedValue of QualifiedSymbol * EDNValueParsed
                | EDNList of string list
                | EDNVector of string array
                | EDNMap of List<string>
                | EDNSet of List<string>
  and EDNValueParsed = 
    struct
        val line: int64
        val col: int64
        val ednValue: EDNValue
        new (ednValue, line, col) = { ednValue = ednValue; line = line; col = col }
        override this.ToString() = 
            sprintf "%A" this.ednValue
    end

These two functions defined afterwards, fail compiling since EDNValueParsed is not seen as defined. EDNParserTypes.fs(41,41): Error FS0039: The type 'EDNValueParsed' is not defined. (FS0039) (EDNReaderWriter)

let getLineColString (valueParsed : EDNValueParsed) =
    System.String.Format("line: {0}, column: {1}", valueParsed.line, valueParsed.col); 

let isNotCommentOrDiscard (v : EDNValueParsed) =
    match v.ednValue with 
    | EDNComment _ | EDNDiscard _ -> false
    | _ -> true

One curious thing, if I remove the lists part definition of the type, it doesn't fail (but obviously fails somewhere else where those definitions are needed)

With this part removed, types are properly defined:

   | EDNList of string list
   | EDNVector of string array
   | EDNMap of List<string>
   | EDNSet of List<string>

What am I missing?

If you have new version of VS you can not have old "pre-installed" version of FSharp.Core (4.0.0.0).

So, reference like this:

<Reference Include="FSharp.Core, Version=4.0.0.0, Culture=neutral,
PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" />

will be a broken.

I wasn't able to reproduce error from the question, but error which I got was pretty straightforward:

Could not resolve this link. Could not find assembly "FSharp.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL"

The type "FSharpList<>" is defined in an assembly that is not referenced. You must add a reference to assembly "FSharp.Core, Version=4.3.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"

after correction the project build without errors.