This message appears when the superuser attempts to unmount an active NFS file system. The busy point is the working directory of a process.
Determine which shell (or process) on the workstation is currently located in the remotely mounted file system, and change--cd(1)--out of that directory. Be wary of subshells (such as su(1M) shells) that could be in different directories while the parent shells remain in the NFS file system.