Your answer must be a date in the correct date format.
This prompt requires at least one selection.
CAUSE: Although this prompt answer works in Strategy Developer, having specified the correct Regional Settings, Strategy Web is taking the default format defined in the Web Preferences.
Customizing the date format with the steps indicated in the following Strategy Knowledge Base technical note does not resolve the issue:
KB12819: How to display the correct customized date format in the calendar (date picker) inside prompt text box in MicroStrategy WebACTION:Select the appropiate language as the Number and Date Format under Project Defaults -> Locale.