I'll explain the ,serialno file in a minute, but as for the 'serial number is corrupt' message, I'm not sure why you're getting that. Since this appears to be a new sim you created, I'd suggest you blow-away this simulator install directory, and then re-install your simulator from scratch.
In a clustered simulator, the ,serialno file contains two numbers. The first entry is the System ID of *this* node (i.e. /sim/node1) , and the second entry is the System ID of its cluster partner (i.e. /sim/node2). If you look at the ,serialno file for the cluster partner, it will have the exact same two numbers, but their order is reversed because it lists *its* System ID first. So, you're going to have to edit the ,serialno file for both nodes of the cluster to make the System IDs unique, and the numbers have to match in both ,serialno files. For example:
# cat /sim/node1/,serialno
# cat /sim/node2/,serialno
Note: Remember that the first entry in each ,serialno file refers to that simulator's System ID. The second entry is its partner's System ID. That why the same numbers exist in both files, but the order they're listed in is reversed.
For the ,sys-serial-num file, you only need one entry. This entry is the serial number of this specific simulator node. Even if its part of a cluster, you only need one entry. For example:
# cat /sim/node1/,sys-serial-num
# cat /sim/node2/,sys-serial-num
Once you have these files modified, shut down your simulators and then re-start them.