"Processing error message" is a predefined property containing a textual description of an error and is provided by Semantic MediaWiki. This property is pre-deployed (also known as special property) and comes with additional administrative privileges but can be used just like any other user-defined property.
Unable to interpret the "2024/02/30" input value as valid date or time component with "Month 2 in year 2024 did not have 30 days in this calendar model." being reported.