No Overload Method for Join takes 4 arguments

this.Parts
    .Join(this.PartInformation, p => p.PartId, pi => pi.PartId, (p, pi) => new
    {
        p.ListId,
        p.PartId,
        pi.PartDescription
    });

I am in a DbContext for my database.  I want to join the part id of one table to the part if of another table to get some information about the part.  However, when I go to put in the lambda query, I tried the linq sql version too, I get the error, "No overload method for join takes 4 arguments".  I have seen lots of examples of this type of query online.  What is wrong with the above?  

I am using .NET 4.6.2, EF6.4, and SQL Server 2016.  It seems to act like the join is for a string because it is looking for method Join(separator).