I can't remove a NFS datastore from an ESX 3.5 build 110268 with this message :
Error performing operation: NFS Error: Unable to Unmount filesystem: Busy
This datastore was mounted on 4 or 5 ESX boxes but I can't detach it from the last one !
As I don't want to reboot the server, is someone on the community has an idea.
I tried with the VI Client and with the esxcfg-nas -d command without success. I tried to restart vmware-mgmt too 
I tried to stop the NFS service on the storage server also (a RHEL 5 box with 800 Go of disk)