All Paths Generating "Page Not Found"

I'm not sure why this started happening, but it might have something to do with my recent upgrade of another module. I'm hoping someone associated with Pathauto can shed some light on the issue.

Following any link to a node with an alias results in "Page Not Found", even though following the actual path (node/###) works fine.
Not sure if this is related or if this disqualifies this as a Pathauto issue, but when I attempt to load any page with an alias (even those not generated by Pathauto), the same thing happens.

If this is not Pathauto, can someone point me to my next steps, maybe?

Thanks!