Hi Josh
You have to cast the INT to NVARCHAR. I have modified your query like belw:
DECLARE @QRY VARCHAR(300)
DECLARE @ORDER INT
SET @QRY = N'SELECT * FROM [dbo].[datalog_574T] WHERE (1=1)'
SET @QRY = @QRY + 'CASE'+ CAST(@ORDER AS NVARCHAR(10)) +' WHEN' + CAST(1 AS NVARCHAR(1))+ 'THEN ''ORDER BY ACCNO'' ELSE ''ORDER BY CALLNO''END'
Regards
Willington