3.16.1.0b01 tunnel to 3.15.1.0b04: expected issue?

Hi,

please ignore this message, that was a tricky typo, found right after I posted the message.
Leaving the rest here given that I posted already. 


I am running 3.16.1.0b01 on my NSM2 and I am trying to establish a vtun tunnel to another node running 3.15.1.0b04.
Unfortunately the tunnel fails to establish.
I looked at a traffic dump and I see:

VTUN server ver 3.X 12/22/2015
HOST: K6LUD-173-31-64-44
OK CHAL: <fielhcfngbdhcmhliolniaehebjadbnk>
CHAL: <dcndoimaodedngjkcehgihdcpnkcpiak>
ERR

We (the guy running the server and I) double checked the settings multiple times. 
I also have another tunnel running towards a 3.15.1.0 server, though.

Any expected non-interoperability between 3.16.1.0b01 and 3.15.1.0b04?
Any other idea how to debug this?

Thanks,
Ludovico