The version number found within the game hasn't been updated yet, but as long as you're downloading it straight from Itch, it should be the latest version.
Also!! Could you please share a screenshot of how you've installed the DLC folder into the base game? I might be misunderstanding your issue, but it looks like you're trying to run the DLC on its own (or possibly in a folder that's either compressed or in the process of uncompressing), which won't work.
Furthermore, was there any additional text that came with the error code? For example, something similar to "OSStatus error -47". Having -47 by itself makes it a bit hard to identify ^^;