When trying to run the CREATE ASSEMBLY code from Chapter 12, page 115 I think I found an error. The code in the book reads:

CREATE ASSEMBLY [SQLPerformance]
AUTHORIZATION [dbo]
FROM FILE = 'D:SQLPerformance.dll'

The keyword FILE isn't used here. It should read:

CREATE ASSEMBLY [SQLPerformance]
AUTHORIZATION [dbo]
FROM 'D:SQLPerformance.dll'