How to change the column property of a column of a database table using SMO.

I use SMO to manage the SQL Server 2005.
I want to change a existing column of a database table to be the same with the other column.
I used the following code but it has an error while calling Column.Alter() function.

public void RepairColumns(object dcolumn)
        {
            try
            {
                Column d_Column = (Column)dcolumn;
                Column l_Column = mServer.Databases[mSMOInfo.DBName].Tables[mSMOInfo.TableIndex].Columns[mSMOInfo.ColumnIndex];
                l_Column.Collation = d_Column.Collation;
                l_Column.Computed = d_Column.Computed;
                l_Column.ComputedText = d_Column.ComputedText;
                l_Column.DataType = d_Column.DataType;
                l_Column.Default = d_Column.Default;
                l_Column.Identity = d_Column.Identity;
                l_Column.IdentityIncrement = d_Column.IdentityIncrement;
                l_Column.IdentitySeed = d_Column.IdentitySeed;
                l_Column.NotForReplication = d_Column.NotForReplication;
                l_Column.Nullable = d_Column.Nullable;
                l_Column.RowGuidCol = d_Column.RowGuidCol;
                l_Column.Rule = d_Column.Rule;
                l_Column.RuleSchema = d_Column.RuleSchema;
                l_Column.IsPersisted = d_Column.IsPersisted;
                l_Column.DefaultSchema = d_Column.DefaultSchema;
                l_Column.Alter();
            }
            catch (SmoException ex)
            {
                throw ex;
            }
        }

If u know my wrong coding, pls point me. 

Thanks ^.^