Does framaroot work on my tablet or phone? 

If your device is listed, it means yes. If it’s not on the list, then try and find out. 

Why did the root-rights disappear after updating the OS? 

Because that hole with which framaroot gave rights was closed by a new patch. 

Framaroot fell when I selected Gandalf exploit? 

Often for the first time Framaroot fails. But do not worry, restart Framaroot and select Gandalf again, the second time should work. 

What do the errors mean? 

All errors less than or equal to 9 mean that your device is not vulnerable to vulnerabilities. If you have a bug # 10, try Framaroot 1.5.3. With all the other errors, you have to try different versions.