Problem with case statement

I have the following Query:

SELECT  CASE WHEN [Question Order] IN ( 6, 11 )
             THEN CASE WHEN [Question Part Label] = 'Other (Please specify):'
                       THEN [Answer Text]
                       ELSE [Question Part Label]
                  END
             ELSE 'replace code here'
        END,[Respondent ID]
FROM    Results
WHERE  [Question Order] IN ( 6, 11 ) AND [Answer Label] = 'Yes'

Now I want to replace this code where it says 'replace code here'

 select         
 stuff((select ','+T2.[Question Part Label]   from Results as T2 
   where T1.[Respondent ID] = T2.[Respondent ID]    for xml path(''), type).value('.', 'varchar(max)'), 1, 1, '') 
   as Label from Results as T1 group by T1.[Respondent ID] 

When I do that I get the following error

Msg 512, Level 16, State 1, Line 1
Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

Sample Data:

Respondent ID  [Question Order]  [Question Part Label]   [Answer Text]   [Answer Label]
124587          6                It was not clear          NULL           Yes
124587          6                Did not Undersstand       NULL           Yes
124589          6                Other (Please specify):   Not enough     Yes
125654          6                Too Fast                  NULL           Yes
124582          11               Not frequent              NULL           Yes

The output Shpuld be:

Respondent ID           [Question Part Label]
124587                  It was not clear,Did not Undersstand
124589                  Not Enough
125654                  Too Fast
124582                  Not frequent

The logic is whenever Question Order is 6 or 11 then I need to dislay the [Question Part Label] if the [Question Part Label] has multiple value for one Respondent_ID then I need to concatenate them but when the value of [Question Part Label] is Other (Please specify): then I need to use value from Answer Text column an

How can I fix this?

DECLARE @Results TABLE
(
    Respondent_ID INT,
    [Question Order] INT,
    [Question Part Label] VARCHAR(40),
    [Answer text] VARCHAR(80),
    [Answer Label] VARCHAR(10)
);

INSERT @Results
    SELECT       124587, 6, 'It was not clear',        NULL,         'Yes'
    UNION SELECT 124587, 6, 'Did not Undersstand',     NULL,         'Yes'
    UNION SELECT 124589, 6, 'Other (Please specify):', 'Not enough', 'Yes'
    UNION SELECT 124654, 6, 'Too Fast',                NULL,         'Yes'
    UNION SELECT 124582, 11, 'Not frequent',           NULL,         'Yes';

WITH x AS 
(
    SELECT Respondent_ID 
        FROM @Results 
        WHERE [Question Order] IN (6,11)
        GROUP BY Respondent_ID
)
SELECT x.Respondent_ID, Label = STUFF((SELECT ',' + CASE 
    WHEN [Question Part Label] = 'Other (Please specify):' THEN [Answer text] 
    ELSE [Question Part Label] END
    FROM @Results 
    WHERE [Question Order] IN (6,11)
    AND Respondent_ID = x.Respondent_ID
    FOR XML PATH(''), TYPE).value(N'./text()[1]', N'varchar(max)'), 1, 1, '')
    FROM x;

Add this where it says 'replace code here'

 stuff((select ','+T2.[Question Part Label]   
        from Results as T2 
        where T1.[Respondent ID] = T2.[Respondent ID]    
        for xml path(''), type).value('.', 'varchar(max)'), 1, 1, '') 

And add T1 as an alias to your result table in your main query.