MongoDB 3.2 replica set with arbiter version 2.6
In general MongoDB only supports mixing adjacent major versions (eg. 2.6 and 3.0, 3.0 and 3.2, 3.2 and 3.4) in a replica set for the purposes of a rolling upgrade to a new version of MongoDB. Mixed version requirements are currently only mentioned in the upgrade notes but I expect the underlying assumption is that new deployments would always use start with the same version.

If you create a new replica set deployment using MongoDB 3.2, the replica set will be using a new election protocol ("version 1") that older versions of MongoDB do not support. For more information, see: Replication Election Enhancements.

The proper solution is to add a MongoDB 3.2 arbiter to your new 3.2 replica set. For any new deployment I would definitely recommend using identical versions of MongoDB to avoid unexpected issues.