NFS File System Considerations
NFS file systems have different locking mechanisms compared to local file systems, which can cause issues with file operations. If /export/build is an NFS file system, try configuring the agent to place the remoting jar file on a local file system to see if the problem persists. This can help determine if the issue is related to the NFS file system. For more details, refer to the discussion on the Jenkins community forum: 
java.io.IOException: Could not copy remoting.jar into ‘/export/build’ on agent.