limits for line loss?

[pfeffernusse]

I've got a MAGIX with a 412, 2 016's, merlin mail, and a D100. All ports, save the 4 analog line ports, are in use. all sets are ~150 ft from KSU. I have a couple of sets at the far end of area acting strange: hot one day dead the next. connections are good. all cable pairs (4) used: 2 analog 2 digital(on one problem - the others are 2pr used). 2 digital sets having problems. one analog set had problem. tone signal bleeds through to all pairs. usually a weak/quiet tone difficult to find is now detectable from 6 inches! Any thoughts?
TIA
Thomas