Avtech 760 lost connection intermittently

I have Avtech 760 connected to Linksys WRT54GS. Everything works fine: I have email notifications, ftp upload, web browser monitoring.
But it's all good for only a day. The next day I try to log in to Video Server E I get " Login procedure failed " error and web monitoring isn't possible either. Both my internal and external ip adresses give me error message. Only option is to reboot the DVR and then it works again for a day or so ( I haven't been checking it every day, but when ever I do, it's unaccessible).

Any thoughts on that??