could not look up internet address for .lan

[idefix]

Hi all,
I installed xfce as a desktop environment. Everything works fine, except that at startup of xfce I always get a message:

could not look up internet address for .lan
This will prevent Xfce from operating correctly.
It may be possible to correct the problem by adding
.lan to the file /etc/hosts on your system

Then I have 2 buttons: "Continue anyway" and "Retry". When I choose "Continue" xfce works fine.
How can I fix this?

My /etc/hosts contains 2 lines:

 ::1     localhost localhost.my.domain
127.0.0.1   localhost localhost.my.domain

In what form should .lan be added?
Thanks in advance for a reply.