It just means 'invalid'. It's not necessarily an error. For example, a firewall filter rule that refers to an address list that doesn't exist is invalid and highlighted in red. That isn't an error - you can create dynamic address list entries based on RADIUS logins, for example, and the rule isn't an 'error' just because at the time you're looking no one with those properties is logged in. Same with a Hotspot associated with an interface that is considered down because it's WLAN interface that no one is connected to - the moment someone connects it stops being invalid.
It's up to you to double-check the relationship between entries that renders them invalid. For DHCP server entries the most likely case is quite simply that you're referring to an IP pool by name that doesn't exist.
Specific answers require specific questions. When in doubt, post the output of "/ip address print detail", "/ip route print detail", "/interface print detail", "/ip firewall export", and an accurate network diagram.