Sounds to me like someone changed one of the columns to require unique values and now, when you are attempting to delete individual rows you're running into a uniqueness error.
Technically, SQL should have prevented the process of setting a unique column while there were non-unique values within it but...
What I would recommend is that you change whichever column has been set to requiring unique values such that it no longer requires this... Delete or change all non-unique values such that all values in that column are unique and then re-create the column rule for uniqueness after that.
While the unique constraint is on the column it will give you that error every time you attempt to remove columns as you will be removing one non-unique row but there will still be other non-unique rows present.
At least that's what it looks like from that tiny screen shot you provided without any additional information to base my assumption on :twisted:
i have seen this problem but that error message can occur if there is a constraint which the deletion violates. A common one might be that a field is set to "NOT NULL".
or otherwise check is there any relation ship with other table....
i want to say Primary key and foreign key relationship .
Completely agree with Permalink. the reason why you could receive such error is when you've multiple entries with the same values and you are try to remove only one of them. as per his suggestion backup your information first and try to delete all records linked to it. you need to do it for all entries in that table, then enforce the uniqueness constraint on your entries after you have resolved the problem.