The version 1.2.6 of Currency Converter for Windows Phone seems to have some issues. Some users are reporting that they get a FormatException error. It seems to affect only those users who have a non-English the region setting. The problem has been identified and a new version (1.3.1) has been submitted and should be available in Windows Phone Store within a week. We apologise for the inconvenience caused but this issue. Thank you for all the feedback.