Phase Approval - not working in PPM5.0

We are on PPM 5.0.

I did the following (for Phase Approval)

- Specified DPR_APPROVAL_HIER as the approval document under "Phase Type"

- Under "Basic Settings > Forms for Printing and Project Status Reports> Activate ...", I activated the document under the relevant project type (both under "Print PDF form" and "Smart forms..." .

At the front end, I assigned the Decision Makers and carried out the required steps.

When I click on "Begin Approval", I get the following message:

"You cannot begin approval without an approval document".

Please advise.