We are having an intermittent problem receiving faxes.  There are certain other veterinary practices that can't fax us and occassionally our branch can't fax us either.  No problems sending faxes.  When faxes aren't received, they are being answered but then the transmission fails.  Can't seem to find any link between being online, on the phone, etc.  We are using a ISDN line from BT.  Have had printer and used for faxing for a year.  Always had problems with certain practices but intermittent problems with faxes from previously fine numbers is relatively new.  Have emailed Dell, tried to find useful assistance on their website and in printer user guide but have had no luck anywhere.  Anyone have any suggestions?  Thanks in advance.