Looks like you have been working with diagnosing and repairing just a loud echo scenario. Have you tried adjusting the echo cancellation coverage as this might be a long echo scenario. The new routers and 12.4 code default to 64ms but older routers were set with 8ms. You can try this command below but it would be best if you post your IOS version so we can give you an accurate command. Also if this is MGCP controlled you should apply the command on the CCM admin page.
echo-cancel coverage 64
Additionally the commands you have added (Attenuation 8, gain -6 and worst case ERL 0) should be validated with a show call active voice during a call experiencing echo. Blindly setting these values is usually not recommended. Here is the document for that below.
Do a sh voice port and verify that the Echo Cancel Coverage is set to 64ms. I believe this is the default in 12.4 but you should verify. If it isn't set to 64ms then set it to that value. Depending on the hardware this can even be configurable up to 128ms (CMM allows that).
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.