Databases do not allow the deletion of rows if those are referenced in other tables with the foreign key constraint. You can turn off the validation of foreign keys in Microsoft SQL databases for the duration of the maintenance with the following script.
--Disable foreign keys on all tables
DECLARE @table_name SYSNAME;
DECLARE @cmd NVARCHAR(MAX);
DECLARE table_cursor CURSOR FOR SELECT name FROM sys.tables;
OPEN table_cursor;
FETCH NEXT FROM table_cursor INTO @table_name;
WHILE @@FETCH_STATUS = 0 BEGIN
SELECT @cmd = 'ALTER TABLE '+QUOTENAME(@table_name)+' NOCHECK CONSTRAINT ALL';
EXEC (@cmd);
FETCH NEXT FROM table_cursor INTO @table_name;
END
CLOSE table_cursor;
DEALLOCATE table_cursor;
GO