Ferret errors

[Jose Antonio Gomez Tejedor <tejedor@xxxxxxxxxxxxx>]

   Hello,
   
   I am just starting on learning Ferret. When doing the following command:
'set data b.cdf', I am getting the error:

   ** unknown netCDF error code:  20
   
   Does anyone know the meaning of this error message, and the way to solve
it?.

   I want to ask if there are any way to obtain more information about
Ferret error messages,

          Thank you,
	  
	       Jose A. Gomez Tejedor