Invalid date error occurred when editing Date Time picker field

Summary

When I choose a date from the date picker, Issue Editor raises an error saying that date format is invalid.

Answer

Set the Date Picker and Date Time Picker to match the format in Jira (System > Look and feel and System > General configuration > Advanced Settings).

Example

System > Look and feel

Time Format	h:mm a
Day Format	EEEE h:mm a
Complete Date/Time Format	dd/MMM/yy h:mm a
Day/Month/Year Format	dd/MMM/yy

System > General configuration > Advanced Settings

jira.date.picker.java.format	d/MMM/yy
jira.date.picker.javascript.format	%e/%b/%y
jira.date.time.picker.java.format	dd/MMM/yy h:mm a
jira.date.time.picker.javascript.format	%e/%b/%y %I:%M %p