Yesterday I was at a client site where everyone prints directly to the printers, rather than sharing via a print server. One of the PCs kept showing a printer as offline, even though everyone else was printing to it. From the PC you could ping the printer and even browse to the builtin web server to see that it was low on cyan.
After chewing on this for quite a while, I found the issue: a checkbox on the Ports tab "SNMP Status Enabled", which when checked (along with SNMP turned off on the print device) will result in the printer being listed as Offline. Once the box was unchecked, it was back online and the customer was back to printing once again.