nfsd hang !!! RPC request reserved -1453504422 but used 116

Hi,

Three days ago, I got the message "RPC request reserved -1453504422 but used 116" in my linux box. When the message issued, my nfsd is not respond.

--- NFS server ---
linux-2.4.27
filesystem : xfs

--- NFS Client ---
linux-2.4.31
Redhat 7.2
application apache-linger-1.3.33

--- Configuration ---
NFS server export option : async, rw
NFS Client mount option : noatime, udp

And a week ago, NFS server was crashed and No ping. I can't find any kernel message dump.

I don't know that above 2 problem is related.

Please help!
Thanks.