Limit patron registration
It would be really nice if Vega Program would prevent a patron from registering for multiple events occurring at the same time, since they cannot possibly attend more than one at a time. An alert - via email, text (when available), or pop-up that either 1) the registration cannot be completed because they are registered for another event or 2) offer to cancel their existing registration and complete the current one.

-
Grace commented
A thought to consider: perhaps it is a parent registering their children or themselves on one card for programs happening at the same time. Parent is registering themselves for an adult program, while at the same time there is a tween program happening. My library has days where we purposely schedule different age group programs to happen at the same time. We have parents registering their younger kids for the kid's program, and their tween/teen for the teen program occurring at the same time.
I think an alert to notify the person there are conflicting programs would be good, but maybe don't stop the patron from completing registration.