If Mosaic still doesn't work, follow the instructions displayed as Mosaic dumps core and send a bug report to mosaic-x@ncsa.uiuc.edu.
If the problem is (1) or (2), your network administrator will have to find some way to fix it.
If the problem is (3), and you're running on a Sun, try the binary named Mosaic-sun-lresolv. If this still doesn't work, or if you're not on a Sun, then contact your network administrator.
Some X servers refuse to run Mosaic when all of the fonts Mosaic requests upon startup are missing. If this happens to you, your X server is either misconfigured or broken. You should probably contact your system vendor. (As a last resort, grab a copy of the Mosaic app-defaults template file and substitute fixed for all the fonts, and try to run with that.)