text: Improper zoning can lead to SAN congestion, which can inhibit remote link communication 
  intermittently. Checking the zero buffer credit timer with IBM Spectrum Control and comparing 
  against your sample interval reveals potential SAN congestion. If a zero buffer credit timer is 
  more than 2% of the total time of the sample interval, it might cause problems. 
  
  Next, always ask your network provider to check the status of the link. If the link is acceptable, 
  watch for repeats of this error. It is possible in a normal and functional network setup to have 
  occasional 1720 errors, but multiple occurrences could indicate a larger problem. 
  
  If you receive multiple 1720 errors, recheck your network connection and then check the 
  system partnership information to verify its status and settings. Then, perform diagnostics for 
  every piece of equipment in the path between the two IBM Storwize systems. It often helps to 
  have a diagram that shows the path of your replication from both logical and physical 
  configuration viewpoints. 