Problems my net n900c on Imac

Time Machine does not good function on the internal drive my net n900 c, wich I have two months now. He makes a complete back up, but after finishing that, there comes a pop up from time machine saying that the back-up is not good and must over. This error repeats every time. This bug is there from the beginning; I have till now not have any good back-up from my harddisk. 

Is this a known bug? Is probabliy a new firmware coming? 



Welcome to the Community.

What version of Mac OS do you run in your system? Is this happening with every Mac you have tried?