For many years, one way for NCSU students to reach WebAssign was via the address "webassign.ncsu.edu". That address seems to not be working today. However you can still get to WebAssign via the address "webassign.net/ncsu/".
I have changed the links on the class website to make them work in this manner. If you have bookmarks to WebAssign that have stopped working, try the address shown in the above paragraph.