Parse error: syntax error, unexpected '?'

[Exodon]

Hi
I tried to install the backup plugin but got this error : Parse error: syntax error, unexpected '?'

Going to tell the steps:

1. Add the plugin to the project via october cms website;
2. Login in the production website and install the plugin;
3. Try to click any kind of update and didn't work and always gave me this error message :
   Parse error: syntax error, unexpected '?'

[panakour]

can you tell me the full stack trace error