System. Web. Services. Protocols. SoapException: Server was unable to

Hello:
We have created a service web that works perfectly while is invoked in the
localhost of the machine of development or from the IE of the servant where
we have published it. Nevertheless, if we create an application client who
does a call to the same one, it returns the following mistake to us:
System. Web. Services. Protocols. SoapException: Server was unable to
process request.> Object reference not set to an instance of an object.
We have tried in another servant and his(her,your) functioning has been
correct. We believe that it has to see with some element of configuration of
the servant or of the IIS but we do not meet on the solution.
If someone has some suggestion...

Thank you very much