APE connection issues.

[Nitro1]

I have been using my Airport extreme with a WD hard drive for a while now and i have been having an issues as of recently that i can not figure out. I take my computer to work and back home at least once a day and when i get home connect to my network and go internet surfing. At first this was not a problem and the TM would back up automatically without any issues. But now all of a sudden for about a month now the back up works for about a week then it stops working. The only way to get the TM to work again is to unplug my HD and replug it then relocate it on my mac and then the back up starts to work again for about 5-10 days then i will need to do it all over again, it is not a big deal but i would like to know why it is doing this? Any idea's or help is appreciated.