Below is a link to a post from a User who states they have a workaround for this issue:
Please note that this potential fix is recommended for new installations not upgraded CMSs.
If this does not resolve the issue, I would recommend installing an earlier version of Xampp that includes Mcrypt.
Version 1.8.12 will not require Mcrypt resolving the issue in the future. There is not currently a set release date for 1.8.12 but we will update our blog as soon as there is more information.
Many Thanks.