I am trying to change the project start date on a grant project. Version 9.2.

I am trying to change the project start date on a grant project.  When I make the start date later than the original date, and also try to add a project manager to the project team, an error occurs referring to the old start date. We have changed the date in all the fields  we can find online in the project area.  Any thoughts? We are on version 9.2.  Navigation: grants > Awards > Project