Getting error in the Email Module

[akkimca]

Hi everyone,

I m using sugarcrm 5.1. and i getting error in the Email module.
when i click on "All Emails" in short cut than i m getting this Error:
Error filling in additional detail fields: Query Failed:SELECT first_name, last_name, assigned_user_id parent_name_owner from users where id = '342a8ed9-c61c-350c-d85b-489619151435'::MySQL error 1054: Unknown column 'assigned_user_id' in 'field list'

i remove the "assigned_user_id" in query so it will give me out put..
so my question is this:
what this "assigned_user_id parent_name_owner" field in query ?? bcoz i dont find any field like this name in database
and if i remove this all "assigned_user_id parent_name_owner", so it will give me any error ??? why this used ??

so pls help me in dt

thanx in advanced