Just recently installed Legacy with CAB2 and Base Version 1.51 on my layout. Lionel Customer Service upgraded the system and installed the Verison 1.51 software. Took out the CAB1 system.
Have one Legacy engine PRR U28c and installed it using the orange module.
Installed my Williams Scale GG1 which was converted to TMCC/ RS 5.0 and used the ERR Cruise M board for cruise control. Named the engine and set the engine number, next identified the engine as an "electric", then the next screen for choosing the control system only showed CAB1, TMCC or Legacy as choices R100 was missing. So I cleared out the information and started over but with the same result.
Then I cleared out the information and this time I bypassed the engine choice screen and went to the screen to choose the type of control system. This time the R100 choice was there. I chose it and R100 was identified in the small tab. Then went back to the engine choice screen and chose "electric". The tab showing R100 changed to TMCC without me doing anything.
So, cleared everything out again and started over. This time I chose the engine type as "diesel" and I was able to choose R100 as the system choice.
In further investigation I found out that the only engine choices that allow you to choose R100 as the control system are Diesel and Steamer. Any other engine choice will not allow you to choose R100.
Why is this important? Because the R100 system choice was put into the Legacy system to have better controll over engines using the ERR cruise boards.
This is obviously a flaw in the Legacy Version 1.51 software.
BTW: This was confirmed with another Legacy user so I know it is not my system.