Confused by to_char

I am am trying to get a day string from a date using to_char ie:

SELECT date1,ti1 ,to1,ti2,to2,adj,ei,eo,to_char('2005-02-07','Day') FROM
vw_times_list1

however I get

function to_char("unknown", "unknown") is not unique

(using to_date does not recognise the date format)

anyone any ideas what I am doing wrong