Hi there,
It sounds like the plugin that you’re trying to upload may not be compatible with another plugin or WordPress itself. Are you able to access your dashboard? If so, try deactivating all of your Plugins, upload and activate your new plugin, then activate the other plugins one by one to see if there is one in particular that is causing the conflict.
If you are unable to access your WordPress Administration Screens, deactivate your Plugins via FTP by following these instructions.
This is a common WordPress error, which means you aren’t alone – you can find a little more information about it here. ??
I hope that helps! Good luck.