I've tried to install a add-on and i got this error: This error is too general and it doesn't say what error.. As first i thought it's because of the missing install callback class/method, but it was uploaded. As next i checked the file because i thought that something was changed while the ftp upload=> also not the error. The problem was, that i assigned a Code Event Listener to this add-on(but it's from an other add-on) because of this, the file was missing and that's why the install didn't work. Wouldn't it be better to show, where exactly the error happened, or to show the class name & method which was tried to access, to make debugging easier? The same is happening with cron entries.