Can't install any plugin : "No valid version available"

Hi, I have a working etherpad-lite instance on a Debian server. When I want to install any plugin (npm install ep_adminpads as root), I obtain the message

npm ERR! code ENOVERSIONS
npm ERR! No valid versions available for ep_etherpad-lite

I have the same problem with all plugins ! I use node v9.10.1 npm 6.0.1 and git up-to-date etherpad-lite 1.6.6 (6dd172d) The server is behind a proxy, but the proxy it is defined in environnement variables.

[jprenaudet]

Same issue for me. For testing I rollback from 1.7.0 to 1.6.6, here is the procedure I use :

git checkout .
git checkout tags/1.6.6
rm -rf ./src/node_modules
rm -rf ./node_modules
./bin/installDeps.sh
npm install ep_adminpads

Error appear with the last command. I resolve it using this :

npm cache clean --force #Not sure if this help
rm -rf ./src/node_modules
rm -rf ./node_modules
rm package-lock.json
rm src/package-lock.json
./bin/installDeps.sh
npm install ep_adminpads

[gllmhyt]

Thank you @GenJin, I did quite the same (with git clean after having saved settings) and it worked right after it!