I don't have the RCA however faced the same issue and it looks like it happens only when we use --version flag to specify the version. I used the path to chart directory which was created by downloading the chart pkg and exploding and it worked like charm.

First Upgrade your tiller

helm init --service-account tiller --wait --upgrade

Then in --version flag use chart version relevant to prometheus version which you are trying to install.

Eg: helm install stable/prometheus --namespace monitoring --name prometheus --version=8.5.0

Here I tried to install 2.6.1 prometheus version.

I see in the helm install code:

# help provides possible cli installation arguments
help () {
  echo "Accepted cli arguments are:"
  echo -e "\t[--help|-h ] ->> prints this help"
  echo -e "\t[--version|-v <desired_version>] . When not defined it defaults to latest"
  echo -e "\te.g. --version v2.4.0  or -v latest"
}

So just in case, do try with: --version v6.7.4 instead of --version 6.7.4.

I think your command is wrong:

helm install -f stable/prometheus/values.yaml prometheus --name stable/prometheus --namespace prometheus --version 6.7.4

Helm install command is:

helm install [CHART] [flags]

So in your case this should be:

helm install prometheus stable/prometheus -f stable/prometheus/values.yaml  --namespace prometheus

-- version is used for chart versions:

  --version string           Specify the exact chart version to use. If this is not specified, the latest version is used

Above command will install Prometheus version that is specified in values.yaml under tag but read this: https://github.com/helm/charts/tree/master/stable/prometheus for full list of parameters.

Use --version "0.15.0" i.e. the version number in double quotes. It worked for me.