If you are trying to pull the config via SNMP through the NCM console and you have verified credentials, you should be able to download the config. However, In your question you say that you are trying to pull it from the "Config Download" in the engineers toolset. Are you running the toolset and NPM/NCM on the same machine?
If you are running NCM on your server and running the toolset on a different machine, your request for SNMP will come from the machine, not the NCM server. Verify that your SNMP config allows the workstation with the engineers toolset to connect and verify that your toolset is configured with the proper RW community strings.
If I remember correctly, in order to download a config via SNMP you must have RW authority.