Types don't match between the anchor and the recursive part in column of recursive query

Question

Given a category @categoryId, the query should recursively navigate to the top most super-category, which has been accomplished.

Now I'd like also to generate all along a string which would be the concatenation of all the CategoryName in the process.

DECLARE @CategoryId AS int = 217;
WITH Categories AS
(
   SELECT ParentCategoryId, CategoryName, '' AS strCategory
   FROM Category 
   WHERE CategoryId = @CategoryId

   UNION ALL

   SELECT c.ParentCategoryId, c.CategoryName,
       (c.CategoryName + ': ' + cts.strCategory) AS strCategory  
   FROM Category AS c
   JOIN Categories AS cts
   ON c.CategoryId = cts.ParentCategoryId
)

SELECT TOP 1 CategoryName, LEN(CategoryName) AS strLength
FROM Categories
ORDER BY strLength DESC

With the above code I'm getting the following error:

Types don't match between the anchor and the recursive part in column 
"strCategory" of recursive query "Categories".

Thanks for helping

Solution

Try changing the query to cast the varchars to VARCHAR(MAX).

Something like

DECLARE @CategoryId AS int = 217;
WITH Categories AS
(
   SELECT ParentCategoryId, CategoryName, CAST('' AS VARCHAR(MAX)) AS strCategory
   FROM Category 
   WHERE CategoryId = @CategoryId

   UNION ALL

   SELECT c.ParentCategoryId, c.CategoryName,
       CAST((c.CategoryName + ': ' + cts.strCategory) AS VARCHAR(MAX)) AS strCategory  
   FROM Category AS c
   JOIN Categories AS cts
   ON c.CategoryId = cts.ParentCategoryId
)

SELECT TOP 1 CategoryName, LEN(CategoryName) AS strLength
FROM Categories
ORDER BY strLength DESC