Lionel Odyssey and ERR cruise

Probably not going to work well. I would expect one to be pushing/pulling as they go in to and come out of curves and hills.  Set both engines to no cruise and run them NOT hooked together.  If they maintain their distance from each other then you should be able to MU them without cruise. 

If the ERR engine is the slower of the two you may be able to use the "Nudge" feature:

“Nudge Mode” Operation

The Cruise Commander has a bit of “play” to allow locos to operate in a lash-up.  At times the “play” is not optimal, so it is possible to match locos a bit closer with the “nudge” mode feature. Remember to lash-up only very similar locos and that it is a requirement that the gear ratios match.
 
Simply try the locos together in a lash-up at slow speeds.  If they buck each other, use the Cruise Commander “nudge” mode to try to match the locos a bit closer.  Nudge mode basically increases the slower loco to match the speed profile of the faster loco.  Although similar to a “stall” setting, the nudge mode is a bit more complex as it calculates the speed profile dynamically to hold the locos in sync throughout the throttle range.

First create a “TRain” with the Cab-1.  Once the locos are operating in TRain mode do the following:

Test run the locos (not coupled) to find the slower loco

Place the slower loco behind the faster one

Get them moving as a train, around 10 speed steps on the throttle

Select the slower loco ENG ID

Press AUX2 4 times, with a 1 second pause between each press

The lights should blink off twice, confirming the loco to be “nudged”

Use the Boost and Brake keys to adjust the slower loco to match the faster one

Press “HORN” to lock the setting in the slower loco

Aux1 will cancel the setting.

Couple the locos together and run as TRain.

To summarize:

Select:  
Slower Engine ID

Activate:
  AUX2 + AUX2 + AUX2 + AUX2  

Nudge:     
BOOST to speed up, Brake to slow down

Save:
        Horn

To clear the nudge settings, select the speed step (32 or 100) on the “nudged” loco.

Note: the “nudge” selection  is stored until changed, and survives power cycling.