PSI: Create project based on EPT with template error

hi,

We are trying to create a project through psi. Whenever an enterprise project type id that is linked with a specific template is provided, we get the following error:

EnterpriseProjectTypeInvalidData

unfortunately the documentation is not very enlightening. If we try to remove the template from the enterprise project type then the creation is done correctly. we have tried using very simple templates (only one task - no assignments) in order to ensure that the data inside the template are valid, and still we are getting this error.

Any ideas? thanx in advance

Spyros