No cluster member after TCPIP update?

[willemgrooters]

I added new hardware to my environment, set up an HP OpenVMS instance on thast system (to install the VSI community version) and set it up as a cluster member, and that worked fine.
Next I upgraded thatr system to the VSI community version (VSI 8.4-2L1) and booted again - and that showed up in both machines: The first machine running VMS V8.4, the second one VMS V8.4-2L1. At that point, the second system was still using HP TCPIP :

$ tcpip sho ver

HP TCP/IP Services for OpenVMS Alpha Version V5.7 - ECO 5
on an AlphaServer DS10 617 MHz running OpenVMS V8.4

$

(where I would expect it to run VSI's version (ECO5F) as stated in the log of installation) and rebooted.
But since then, the system will NOT boot into the cluster: the first machine still mentions the new one, but as BRK_NON, where the now one itself as member ( running VMS V8.4-2L1) and the first one running VMS V8.4-2L1 as well (which has not yet been updated) but no mentioning of being active or inactive member.

More: it still shows HP's TCPIP version, though the VSI version is installed...

I shutdown the second machine to power down, and restarted it, but the problem remains the same: The second machine will not add itself to the cluster. However, this does not seem to be a conection problems since both machines can be accessed, from the LAN and between eachother (both SSH and DecNet access succeed).

The system parameters for clustering have not been changed, and the second system has booted into the cluster before (otherwise the first one couldn't have mentioned the VSI community version), so what caused the sudden inability to connect to the first system?

Added in 32 minutes 29 seconds:
???? After changing cluster parameters (enabled LAN as cluster interconnect) it seemed to work again. But this was not needed in another machine that I upgraded earlier...And since connection was fine before, what caused this? Was it the update of TCPIP (still showing HP TCPIP version 5.7 ECO 5...)