This is usually because the place where your crontab-ui is installed does not give access to others. It can be resolved by either __giving permission__ to the user (Recommended) or running crontab-ui as root. Refer [this](https://github.com/alseambusher/crontab-ui/issues/8)
__crontab-ui stopped working__ - It can happen that your crontab-ui can stop working for some reason like adding incorrect jobs or timings. You can try resetting crontab-ui by running `crontab-ui --reset`.