Schema not loading

Dear Experts,

We are working on NW 2004s EP 7.0 and we recently upgraded to SP 13.

When i open existing XML projects in xml form builder the schema is not loading.

Even if i try to create new project also it is not showing anything in the "Data Model" tab.

What could be the reasons???

Thank you very much in advance for your valuable inputs.

Best Regards,

Satya