What is the MOST likely cause if a server can ping local subnet servers but not others?

When a server can successfully ping other devices within the local subnet but cannot reach those on different subnets, the most plausible cause is a misconfiguration of the default gateway. The default gateway is a critical networking component that allows devices on one subnet to communicate with devices on another subnet. If the default gateway is incorrectly configured, the server lacks a valid path to forward packets to external networks, which results in failure to ping servers located beyond its local subnet.

In the case of the other options, while they address various network issues, they do not directly explain the specific scenario presented in the question. For instance, being not joined to the domain wouldn’t impact the ability to ping servers within the same local subnet. A misconfigured subnet mask could lead to some problems, but it typically affects the server's perception of its own network inclusion and doesn't usually restrict local ping success. WINS misconfiguration primarily impacts name resolution in Windows networks, but it would not prevent direct IP communication locally or across subnets.