Remove First comma character from string in SQL Server

Output as follows

, RFPFF 16, R-AFF 16, RFPFF_C 6

in that above output i want to remove the first comma for that i written query as follows.

My sql query as follows

select substring(ltrim(rtrim(cmn_minor_code,(LEN(cmn_minor_code)))) as Course_Name,cbm_batch_id as Batch_ID from co_batch_master where cbm_active <> 'D' and cbm_batch_start_dt = '01/13/2014' and cmn_minor_code in('RFPFF') 

when i execute shows error as follows The rtrim function requires 1 argument(s). for that how can i write the sql query.

Regards,

Narasiman P.