Answer
This is almost always a credentials issue with the IFSPRINT account rather than a genuine licensing problem — Print Agent's configuration can auto-populate what looks like an already-entered (encrypted) password even when the underlying password field is actually blank, which commonly happens right after an uninstall/reinstall of Print Agent. Even if everything else in the configuration looks correct, re-enter the actual IFSPRINT user's password explicitly in Print Agent's setup — this resolves the license error in cases where the password field only appeared to be populated.