Hi Aaron, principally, the library is not present on all machines, even with similar installations........see this from post #11 of the linked thread.

it was working fine on the laptop i made the workbook on, but when i opened it up on another, almost identical machine it would throw a "can't find object or library" error.
If you want to use the native calendar control on a file that will be used on many machines you will run into this problem quite often. The only thing you can do is make sure the calendar control is installed on every machine it gets used on........an overwhelming caveat in most cases...