I now have Leopard and various versions of Snow Leopard installed on my Mac Pro and I get the following results:
All versions can mount a remote OS 9 volume or folder. Leopard can write files to the mounted volume without any difficulty. Some versions of Snow Leopard can write some files at a first attempt but some of these appear empty or corrupted.
I eventually found I could get consistent satisfactory results by using a bash script to write about 40kB to a dummy file twice. After this further files can be written without any difficulty until the connection is terminated. Whist this is slightly tedious I can live it.
Further insights or fixes would be of interest to me.
Here is my bash script:
open 'afp://user-name:password@###.###.###.###/volume/web-pages'; sleep 1; f(){ echo {a..z}{A..Z}{z..n} > /Volumes/volume/web-pages/dummy-file; }; f; f