Hi Thenmozhi,
With respect to the stated issue, can you carry out another test:
Navigate to the project in CA PPM and go to the team tab
Instead of adding a resource, try to add a role and check if you are able to add the same. This will help you segregate the issue.
Secondly you had mentioned, the issue occurs for few projects, so in other projects where you are able to add resources, can you add the same resource, which is causing the error for the project - Cleo Vl Trader
Also with the affected projects, how were they created, from templates or through XOG
We further observe that a support case is also raised for this issue, under your name, presently. It would be helpful to investigate the issue in details and as a support case, wherein an engineer would get in touch with you. Since, it involves checking configuration, page layout, etc.
Regards,
Samik