Thanks again Santiago,
forgot to mention that the task works fine in the DEV environment, but not in PROD - so the folder structure should be fine but after trying several more things today we have still not managed to resolve the issue. Both environments are identical as far as we can ascertain and we have validated that the a/d account running the job has appropriate permission on the server and in BPC.
We are looking to reregister the ddls involved tomorrow, but after that are starting to run out of ideas......any other ideas ?
Dave