xp_regread does not return the right value

[Yale]

i have the following code --

DECLARE @test varchar(20)
EXEC master..xp_regread
@rootkey='HKEY_LOCAL_MACHINE',
@key='Software\Microsoft\Windows\CurrentVersion\Uninstall\{90510409-6D54-11D4-BEE3-00C04F990354}',
@value_name='DisplayVersion',
@value=@test OUTPUT
SELECT @test

@test returns "NULL" when it should be = 10.1.2514... why does this happen? how do i resolve this one?