I’m happy to report that this issue (“Not a valid date” “property ‘GetFormattedDateStr’ is null or undefined”) can generally be fixed very quickly.
Usually such issues are introduced during Windows updates when Microsoft changes Internet Explorer settings by restricting security for running scripts.
A standard solution for this is to add the application URL to the trusted sites list of the Internet Explorer and then set the security level for the trusted sites to Low or Medium-Low.
