This is as yet another update on this, just in case it is helpful to anybody else here.
Xerte is still running slow even after creating a firewall rule to let Xerte traffic go unchecked but at least it is no longer blocking the method GET any more.
I've noticed another glitch, though, to do with uploading pictures.
I've created a project with one object (media\Advanced Image) and uploaded a picture with spaces in the name and it seemed to upload fine and I've checked that the file was really uploaded to the server with the correct name but when I've tried to play the project back I've got an error 404 object unreachable for the picture.
I then edited the name of the file directly on the server, edited the project and pointed to the file already on the server and this time round it did work.
Not sure if this is still related to the firewall issue or not. Still investigating.
Xerte does not recognize any of my previous projects but, again, they were only tests and it is not a big deal for me but may be for others.
Cheers,
Marta