Open Transport SNMP extensions prevent AppleTalk port selection in Mac OS 8.5?

After updating to Mac OS 8.5, you may be unable to select the AppleTalk port (typically the Printer port) from the Chooser. Instead, you'll get a message that reads: "The printer port or modem port you want to use for <printer name> is not available because AppleTalk is selected or another application is using the port. Use the Chooser to disable AppleTalk or close the other application." This is especially likely if you are using Epson Stylus printers. It happens even though AppleTalk is apparently off.

We have previously covered reasons that this might happen (see a and b). But this 8.5-specific instance may be due to a new cause. In particular, two readers (Ceci Land and Arthur Wiese) both found that deleting two Open Transport extensions, Open Transport SNMP and OpenTptSNPLib, eliminated the problem. These extensions should not be needed, and may not even get installed in your System Folder, unless you are on a Simple Network Management Protocol (SNMP) network.