Tim Mackey's Weblog

say you wanted to change a BIT column to a NVARCHAR column, and the BIT column has a default value set to 0 or 1.  you can't run the following statement or you get a dependent object error.

alter table TABLE1 alter column COL1 NVarChar(MAX)

so i found this solution here, after you've run the query below, you can alter the column as above.

DECLARE @df SYSNAME

SET @df = 
 (SELECT OBJECT_NAME(cdefault) 
  FROM SYSCOLUMNS 
  WHERE id = OBJECT_ID('dbo.TABLE1') 
   AND name = 'COL1') 
IF @df IS NOT NULL 
 BEGIN 
  EXEC sp_rename @df, 'df_to_drop', 'OBJECT' 
  ALTER TABLE dbo.TABLE1 DROP CONSTRAINT df_to_drop 
 END