User unable to "Assign" PPM Resource Pool assignments

We've got something odd happening between our DEV and TEST environments.

User is attempting to Assign assignments within a PPM Resource Pool.

Our DEV and TEST Environments are configured the same. The same test user account is being used in both environments. However, in the TEST environment, the "Assign" button is grayed out and not available unless the user is a member of the Resource Pool. In the DEV environment, the user is NOT a member of the Resource Pool, but the button is available.

Any ideas on what might be causing this?

Thank you!

~Lorie