monsieur.d: I too was having the same problem as you and compaqdrew the first poster in this thread. What I did is I followed rumar4u's post above, however that did not fix it at least not all the way. I searched a few more forums for this issue and found out the the Time Machine program is linked to your network connection in that it needs a unique identifier in order to operate. See the attached link to that thread for more information on it, as I'm not that familiar with mac yet but I'm learning. http://forum.osx86scene.com/viewtopic.php?f=3&t=109&start=45&st=0&sk=t&sd=a
After reading this thread I realized that my computer has an onboard lan connection ( as most do ) but it's not connected due tho the fact that i connect to my network through a usb network card. During my first attempts to use Time Machine I had the USB network card removed and my USB disk drive connected which resulted in the error. Once I connected the network card and the disk drive at the same time the Time Machine app started to work as designed. I have attached a screen shot of my desktop to show you that it is indeed working. I hope this helps, good luck.