Rename Field And Add Field With Same Name In One
Couple of things...

The sp_rename procedure is in the sys schema, not dbo.

Second, if you execute a stored procedure in a batch, then you must use the EXEC keyword.

Try changing your code to this:

CREATE Table TMI (empName varchar(500), userID varchar(100), TV float)

CREATE NONCLUSTERED INDEX eNIndex 
ON TMI (empName ASC)

EXEC sys.sp_rename '[dbo].TMI.TV' , 'OrigTV', 'COLUMN'

ALTER TABLE [dbo].TMI
ADD TV float;