I asked this question here and somebody suggested to me that I should asked here.
A friend of mine installed an app called Button Savior (non root) from google play and then decided to uninstall it for whatever reason, but he was not able to uninstall it from his phone, he then asked me to help him to uninstall it from his phone. I searched in google for how to do it, and I found this link.
On this link it was suggested that I first should remove the app from the device administrators list (settings - security - device administrators) and then and uninstall it and if this fails then I should reboot the phone into safe mode and repeat the process. I tried both methods but when I try to remove the app from the device administrators list the setting crash and I got an error message "unfortunately setting has stopped working".
Any suggestions to resolve this issue ?