Trying to create/update customer with InvalidRemoteCallException

Hello,

when i use AX 2012 Webservice i am able to read a customer (CustCustomerService.read), but i am unable to read nor update (CustCustomerService.create, CutCustomerService.update) with the following error:

{System.ServiceModel.FaultException: Exception of type 'Microsoft.Dynamics.Ax.Xpp.InvalidRemoteCallException' was thrown.

Any idea?

Thanks in advance