What does this tell you guys? (E420R)

WARNING: /pci1f,4000/scsi3/sd0,0 (sd0):
Error for Command: load/start/stop Error Level: Retryable
Requested Block: 0 Error Block: 0
Vendor: IBM Serial Number:WARNING: /pci:
Error for Command: load/start/stop Error Level: Retryable
Requested Block: 0 Error Block: 0
Vendor: IBM Serial Number:
Sense Key: Not Ready
ASC: 0x4 (LUN not ready), ASCQ: 0x0, FRU: 0x0