Thanks for the prompt response - wow, it's the middle of the night here! :)
I tried again and success! I've got a couple of nested loops - the outermost is "while plank storage not empty". Within the loop he's going to storage (log), taking a log to the sawbench, using it, then an inner loop 1 - pick up planks until hands full followed by inner loop 2 - take planks to plank storage until hands empty.
I'm sure this is what I tried before, but can't argue with the results - it's working perfectly, thank you - looks like it was my mistake somewhere.....
Cheers, clumsy.