The following error was encountered while changing the collation: <0s>.

The collation was not changed because of the underlying problem described in the message.  Changing a column's collation is akin to changing its data type.  That is, after you change the collation, the Visual Database Tools validate the column's data type.  This validation can uncover a number of problems, including:

• The modification enlarges the column, which in turn enlarges an index beyond the maximum size for indexes.
  
  
• The modification is incompatible with existing data values in the column.

Choose a different collation for the column or fix the underlying problem.