TM server client does not adhere to project

I added a TM from the server of a client to a existing project through GroupShare and with the first file all went well, but adding a new file to to the project I get a message saying "error using the translation provider" (o similar, I have the Spanish version of Trados). So I set up a new project, adding the TM of the server of the client again and same thin happens. Does anybody recognise this or can help me out with this. I redid the whole proces various times and it is driving me nuts. Thanks!