[Koha] z39.50 search not working

A couple weeks ago, I was in the middle of cataloging a stack of books. The z39.50 search function worked for one book and then on the next book, it stopped working and I haven't yet figured it out. I usually use the Library of Congress, Biblios, and Access PA z39.50 sites. The messages I'm getting are: "connection failed to 1x2.loc.gov" and "nothing found". There have been no new security things or firewalls installed (this is a school computer). And it literally happened from one book to the next. Any ideas? Thanks, Shelley