Whenever U start any app, including 2go, WhatsApp and Opera Mini, they always show invalid SIM certificate or application errors. What should I do?
All my applications in the NokiaX2-01 are corrupted including Opera Mini.
It seems to me that you are trying to install and using the mentioned apps from third party sources.Try uninstalling them and get it from Nokia Store.
If the problem still persists,try factory reset (backup your data prior doing this).
hard reset or update firmware then try again