Originally Posted by rharv
Usually caused by Audio Driver.
What are you using?
If external (as suggested in the error(Undefined External error") - was the interface turned on before you opened PT?

Or possibly, is it in use by another app (some other music app open and using it?)
Yep, generally caused by the audio driver. Go to Options > Preferences > Audio then set the driver type to Windows Audio or MME. If you generally use ASIO, it's best to only use it when recording and when all other audio apps are closed, as ASIO drivers tend to lock themselves to one app at a time.

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