Due to the current gap in continued funding from the U.S. National Science Foundation (NSF), the NSF Unidata Program Center has temporarily paused most operations. See NSF Unidata Pause in Most Operations for details.
I have regenerated the files below. These are linked from http://www.unidata.ucar.edu/packages/netcdf-java/Please let me know if you have any further problems, although you might want to try using ftp directly.
ftp://ftp.unidata.ucar.edu/pub/netcdf-java/v2.1/netcdf.jar ftp://ftp.unidata.ucar.edu/pub/netcdf-java/v2.1/NetcdfJavaUserManual.pdf
netcdf-java
archives: