Changing Char/NChar Column From NOTNULL To NULL

Hi I have a table, which contains Char and NChar NOT NULL columns
Now I need to change it to NULL, when I use the following command, it fails for the following error,

The command I used,
ALTER TABLE <TableName>
ALTER COLUMN <ColName> CHAR NULL
ALTER TABLE <TableName>
ALTER COLUMN <ColName> NCHAR NULL


Msg 8152, Level 16, State 13, Line 1
String or binary data would be truncated.
The statement has been terminated.

But for the same table, the below command executes fine,
ALTER TABLE <TableName>
ALTER COLUMN <ColName> SMALLINT NULL


Also I can change the NULLABILITY from NOTNULL to NULL using Enterprise Manger, editing the table using Table Design and selecting Allow Nulls option.

I need a script to accomplish this task.

Any help would be greatly appreciated.


-Senthil