The info in this link may be of interest to you with your fax "out of memory" problem. Click on the Case 3: Fax operation in progress link
(For some reason the link sends you to the bottom of the page. Scroll up to the top to find the abovementioned case 3 link)
As to the "poor line condition" it may also be that you have a faulty line. If you can, connect a corded telephone in place of the fax machine and "listen"for any noise on the line (pick up the receiver, break dial tone by dialing a single digit). If there is noise present go to the first point where the phone cable enters the premises (if there is more than one phone point) and disconnect all the other points so that the line is only connected to that one point and listen there for noise. If it is noisy then you most probably have a line fault and need to contact your phone service provider regarding a repair. If it is quiet there then you may have either faulty internal cabling or phone sockets. Take pictures of the wiring before and if you disconnect any wires in the sockets. That way you have a reference when you go to reconnect them.
As an aside, depending on your location try to find out if your phone service provider has a fax test line. Here in Australia one carrier (Telstra) has this service where you send a test fax to a test number and it responds within 5 minutes (by fax) detailing your fax service. e.g. whether it is set up correctly, transmitting at the correct levels etc. and what needs to be done to your fax machine to have a satisfactory fax service if you haven't got one.