I have also face the same issue during my Redmine initial setup stage.There are many possible reasons.
1)This might be due to a data discrepancy.Change your mysql
dump and try again.
2)Check whether proxy
is set in the server.Otherwise it won't fetch data from google maps and charts will not get generated.
3)Other possibility is plugin compatibility.A new version of EVM
plugin is available in Git.Please download and install it and try again.https://github.com/imaginary-cloud/redmine_evm