I expect this will be fixed shortly, but if an assignment is pending, students should contact their professors. Faculty may be able to upload articles to WebCT if necessary. Also most electronic reserves are also available in print here in the library for those who can visit.
I'll update with more information as I get it.
Update (AM, 4/18): All back to normal now. No hard info on what happened, but it seems to be a software glitch of some sort.