No such function 'to_char' with the specified attributes

Hi,

I'm getting this error:  "No such function 'to_char' with the specified
attributes" when trying to select a timestamp type field.  For example:
"select  to_char(col_name, 'MM-DD-YYYY') from table_name".  Is there
somebody that can help me with this?

Thanks,
Yadira