Sql Server Service Pack 3 Update, Delete Question Or Problem

hi all
i am trying to update or delete a row/record in table cptcodes
the error i am getting is

key column information is insufficient or incorrect to many rows
were affected by update....

can you tell me wat causes the above Error
this is a new table no primary keys set or index's or constraints just a
single table with some data
in it...all columns are char nulls allows except the key field but no
primary set as yet

thanks for the help
dave