This message comes from the NFS server when it receives a request with unrecognized or incorrect arguments. Typically, it means the request could not be XDR decoded properly. This error can result from corruption of the packet over the network, or from an implementation bug causing the NFS client to encode its arguments improperly.
If this message originates from a single client, investigate that machine for NFS client software bugs. If this message appears throughout a network, especially accompanied by other networking errors, investigate the network cabling and connectors.