Only one clustered index can be created on table <Tablename>. (Visual Database Tools)

A clustered index sorts and stores the data rows in the table based on the index key values. Therefore only one clustered index can be created on each table because the data rows themselves can only be sorted in one order.

To create a different clustered index on the same table, change the Create as Clustered property setting on the existing clustered index before creating the second index.

For more information, see How to: Change Index Properties (Visual Database Tools) and How to: Create Clustered Indexes (Visual Database Tools).