This exception occurs when attempting to start a node in WebSphere, using the startNode.sh (Linux) or startNode.bat (Windows) commands before a node has been federated into the dmgr. This exception occurs because the "nodeagents" directory is created after the node has been federated into the dmgr. The solution to this exception is to federate the node into the dmgr, which will create the "nodeagents" directory, and then this exception should no longer occur.
ADMU0111E: Program exiting with error: java.io.FileNotFoundException: was_home/profiles/your_profile/config/cells/your_cell/nodes/your_node/servers/nodeagents/server.xml (No such file or directory)
If you are not familiar with what a node is, or what the different between a node and a node agent is, refer to understanding the difference between a node and a node agent in WebSphere.