I recently built a stand-alone project server 2013 farm by installing SharePoint 2013 and Project Server 2013 with SP1. I ran the PSConfig.exe to finish the process. 

When I tried to browse the PWA after all of the above, I ran into below error:

Derived method 'RequiresWebPartClientScript' in type 'Microsoft.Office.Project.PWA.WebParts.PWAPart' from assembly 'Microsoft.Office.Project.Server.PWA, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c' cannot reduce access SharePoint Server 2013 version: 15.0.4420.1017 Project Server 2013 version: 15.0.4569.1506

Rule of thumb:

SharePoint Server and Project Server must be at same service pack level when you build your farm. In my case, the client had given the source for “SharePoint Server 2013” and “Project Server 2013 with SP1”. I didn't notice this at the time of install and ran into above error.

Solution:

I installed Service pack 1 for SharePoint Server 2013 (it took 3-4 hours for me, so be patient :) ) and ran PSConfig.exe to configure it.

NOTE: Just after installing Service Pack 1 for SharePoint Server 2013, when I tried to browse the PWA, it came up fine with no errors. However, you must have to run PSConfig.exe at the end regardless. Otherwise, you will run into different issues later on.

Hope it helps! If you have any questions please contact us.