Error 24000 when trying to use hierarchyid

Question

I am having issues when I try and generate hierarchyid in my application. Specifically, I cannot seem to have more than 16 children per node. Here is the code that I am trying to use for my stored proc (this is for a test table that just has an hid field, and a content field:

create PROC testAdd (@parentid hierarchyid, @content varchar(10)) 
AS
BEGIN
    DECLARE
       @parentNode hierarchyid , 
       @lc hierarchyid;
    SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
    BEGIN TRANSACTION;
    SELECT @lc = MAX (hid)
      FROM testing
      WHERE hid.GetAncestor (1) = @parentid;

    INSERT INTO testing (hid, content) 
    VALUES ( @parentid.GetDescendant(@lc, NULL),
    @content) ;
    COMMIT;
END;

Here is how I get an error:

1. Run INSERT INTO testing (hid , content) VALUES (hierarchyid::GetRoot () , 'a') ;
2. Run EXEC testAdd '/' , 'a'; 16 times.

The error I get looks like:

Additionally, I attempted to run the second code snippet from this answer, and it broke immediately.

What could be going wrong?

Update: I have already uninstalled VS 2015, and the CLR data types for sql server 2014 and replaced them with an older version to no avail.