Forum Attachments suddenly stopped working
 

Using file system as storage type.

vBulletin 4.05 Suite but only forum enabled.

Was working fine up until todat. Now suddenly uploaded PDF attachments yield a 404 not found and uploaded images don't display.

What would cause this and where do I start to try to troubleshoot it?

I have limits for new members but not for other members and in any case I am the admin/owner with no limit on number or total size of attachments.