Here is the quick tip to overcome this issue.
1. Simply login to your FTP and rename the specific wordpress plugin folder which causes the issue. (illustration shown below for akismet wordpress plugin, not the plugin causes the issue in your site.
2. Rename the plugin which creates issue.
Once you renamed it, the specific plugin got deactivated in wordpress backend automatically and you may able to login to your wordpress dashboard and troubleshoot or resolve the specific issue.