>Hi
>
>I worked out that you have to implicitly use @LockOwner = 'Session', or you have to encapsulate the entire sp_getapplock/sp_releaseapplock code within a transaction. Typically, this requirement is not mentioned in any of Microsoft's SQL help files, I found this out via a search on the internet.
>
>Regards

on BOL

[@LockOwner =] 'lock_owner'

Is the lock owner. lock_owner is nvarchar(32) and can be Transaction (the default), 
or Session. When the lock_owner value is the default, 
or when Transaction is specified explicitly, sp_getapplock must be executed from within a transaction.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/tsqlref/ts_sp_ga-gz_5gh5.asp