SQL Server 2005 returning <Unknown(-16)> while using FOR XML PATH('')

Question

When I use FOR XML PATH('') in the following query, the role values come back fine but for each result the FirstName value is <Unknown(-16)>. Here is the query:

SELECT role, STUFF((SELECT ','+FirstName FROM Employees WHERE role = 'Engineer' FOR XML PATH('')),1,1,'') AS names FROM Employees GROUP BY role

I have tried to find this error code online but have had no luck, has anyone seen this error before in SQL Server and knows how to resolve it?

Update: Just to clarify, if I reduce my query to just this I can still reproduce the error:

SELECT ','+FirstName FROM Employees WHERE role = 'Engineer' FOR XML PATH('')

So this may be an environment issue. I am on SQL Server 2005 SP2. Also note that I am running the query via JDBC (not sure if this matters).

Answer 1

I tried this but didn't get any error (SQL Server 2005 Developer x64):

DECLARE @Employees TABLE
  (
   Firstname nvarchar(50),
   ROLE nvarchar(50)
  ) ;

INSERT @Employees (Firstname, ROLE)
  VALUES ('Andreas', 'Engineer') ;
INSERT @Employees (Firstname, ROLE)
  VALUES ('Michael', 'Engineer') ;

SELECT role, STUFF((
                    SELECT ','+FirstName
                      FROM @Employees
                      WHERE role = 'Engineer'
                   FOR
                    XML PATH('')
                   ), 1, 1, '') AS names
  FROM @Employees
  GROUP BY ROLE ;

It correctly returns the following:

role             names
---------------- -------------------
Engineer         Andreas,Michael