Hi tomcmars,
It looks like the Platform wasn’t able to successfully build your package. Please see this post that talks about the issue you’re having: Build Error: Date-Manip 6.82 for Perl 5.28.1 on Windows
You should have received an error message when you were trying to state activate the project, but it could have been a bit cryptic so your confusion is well placed. We are actively working on improving our error messages.
In the meanwhile you can fix your project from the command line by updating your package to a working version by using these commands (make sure you cd into the folder that has the activestate.yaml in it first):
state package update Date-Manip@5.54
state pull
state activate
Let us know if you still have problems.