I have one sensor that does not auto-ID, but others do.

First, be sure you have narrowed the issue to the sensor by:
1) Trying a different sensor with the same interface and software.
OR
2) Trying the same sensor with a verified interface and software.

Occasionally, the memory on an auto-ID sensor is corrupted and it does not ID properly. It is possible to reset this information to factory settings with the following steps:

In Logger Pro:

1) Connect the sensor to the interface.
2) Choose Sensor Setup from the Experiment menu, and choose your interface from the list.
3) Next to the correct channel, choose your sensor from the drop-down list.
4) Choose "Calibrate" from the sensor drop-down menu.
5) Choose "Set Sensor Factory Defaults" from the Calibration Storage tab, and choose the appropriate switch setting if prompted.
6) Choose OK.
7) Choose "Write" from the alert window.

In LabQuest:
1) Connect the sensor to the interface.
2) Choose Sensor Setup from the Sensors menu.
3) Next to the correct channel, choose your sensor from the drop-down list.
4) Choose OK.
4) Choose "Calibrate" from the Sensors menu and choose the correct sensor.
5) Choose "Set Sensor Factory Defaults" from the Storage tab.
6) Choose OK.

If your sensor is an auto-ID sensor and it still fails to ID, it may need to be repaired.

See also:
TIL 1800: Why doesn't my LabQuest unit recognize auto-ID sensors?