Unlock MIME problem

I bought a "Chilkat 1-Developer Email License" in 2015 and have been using it successfully. This code works with no problems:

success = mailman.UnlockComponent("MyUnlockCode")

Some of the emails I have been trying to decode are now coming as *.eml files so I tried to follow the example here: https://www.example-code.com/vbnet/mime_extractFiles.asp

However, the following code:

Dim mime As New Chilkat.Mime
Dim success As Boolean
success = mime.UnlockComponent("Anything for 30-day trial.")

returns False for Success, regardless of whether I use my unlock code or just leave as default from the example. It recognises the MIME class with no problem.

Do I need to buy another different component to activate MIME? I can't see it in the list of products here: https://www.chilkatsoft.com/products.asp

Do I need to buy a bundle? If so, can I upgrade me existing licence or is it too old?

Thanks!