Installed anything new recently? V38 corresponds to Workbench 2.1 and I'm fairly confident that diskfont.library was updated between then and 3.1
Maybe there's something (badly-written) added to your startup-sequence/user-startup that requires V38 of diskfont, rather than V38 or higher.
Also check LIBS: to see that you have diskfont and that it's not corrupt. Copying it over from the original disks might not be a bad idea.
