The whole error is probably visible in the Chrome Dev Console. It usually means that the JavaScript for the plugin is invalid or couldn’t be found and therefore couldn’t be loaded.
The real error is probably in the Grafana server logs. Here is an example error where I haven’t built the JavaScript for a plugin so it couldn’t load:
EROR[03-31|17:27:09] Failed to start plugin logger=plugins.backend pluginId=grafana-oracle-datasource error="fork/exec /home/daniel/dev/go/src/github.com/grafana/plugins/oracle-datasource/dist/oracle-plugin_linux_amd64: no such file or directory"
Can you see an error in your logs?