Stored procedure runs fine from SSMS but fails when called from the C# app

DECLARE @tableName VARCHAR(50), @indexName VARCHAR(100), @frag FLOAT, @dSQL NVARCHAR(MAX)
DECLARE indexCursor CURSOR FOR 
SELECT o.name, i.name, avg_fragmentation_in_percent
  FROM sys.dm_db_index_physical_stats (DB_ID(), NULL, NULL,NULL,NULL) ps
  INNER JOIN sys.objects o
    ON ps.object_id = o.object_id
        AND o.type = 'U'
  INNER JOIN sys.indexes i
        ON ps.object_id = i.object_id
        AND ps.index_id = i.index_id
  WHERE i.name IS NOT NULL --AND avg_fragmentation_in_percent > 7
OPEN indexCursor
FETCH NEXT FROM indexCursor INTO @tableName, @indexName, @frag
WHILE @@FETCH_STATUS <> -1
BEGIN
 SET @dSQL = ''
 IF @frag BETWEEN 5 AND 30
 BEGIN
  SET @dSQL = 'ALTER INDEX ' + @indexName + ' ON ' + @tableName + ' REORGANIZE'
 END
 IF @frag > 30
 BEGIN
  SET @dSQL = 'ALTER INDEX ' + @indexName + ' ON ' + @tableName + ' REBUILD'
 END
 IF @frag < 5
 BEGIN
  SET @dSQL = '-- INDEX ' + @indexName + ' ON ' + @tableName + ' did not need defragging'
 END
 EXEC sp_executeSQL @dSQL
 PRINT @dSQL 
 FETCH NEXT FROM indexCursor INTO @tableName, @indexName, @frag
END
CLOSE indexCursor
DEALLOCATE indexCursor

Your proc is a bit of a mess and hard to read. This should get you what you need though. I added a little logic in the middle that determines if the index should be reorged, or rebuilt.