You really need to provide the exact error message. If the error message is "A Critical Software Update is Required", then you need to try to reinstall macOS over top of itself. No matter what you need to have a good Internet connection in order for macOS to download the required software for the Touchbar. If that does not work, then the laptop may have a hardware issue that is affecting the Touchbar which will require a repair by Apple or an Apple Authorized Service Provider. In the mean time you should be able to boot into Safe Mode in order to keep using the laptop in a limited fashion so you can at least make sure to have a good backup.
If you have some other error, then you need to give us the exact error message since it is difficult to advise you when we don't know what the error is. Each error condition is different and may require entirely different advice.