Hey Steve,
16 is 0x10 in hex, which if you look in TurboActivate.h you'll see means TA_E_INVALID_FLAGS:
/* MessageId: TA_E_INVALID_FLAGS
MessageText:
The flags you passed to CheckAndSavePKey(...) or UseTrial(...) were invalid (or missing). Flags like "TA_SYSTEM" and "TA_USER" are mutually exclusive -- you can only use one or the other.*/
That's because you didn't pass in a flag (you passed in a version GUID). Your call should be like this:
hr = UseTrial(TA_SYSTEM);