If you are using FogBugz On Demand, disregard this guide and contact us. This article is meant for Licensed FogBugz.
You may have changed the date format on your Windows FogBugz server, but it continues to show up in the old date format. This is because IIS sometimes uses the locale customization settings for the FogBugz user in IIS and not the current logged on user.
To work around this make sure the date format for short and long is set correctly in the HKEY_USERS/.Default/Control Panel/International registry hive. Also, you will have to change it for all of the HKEY_USERS/[LONG SID STRING]/Control Panel/International hives too. Each of the long SID (or unique id) strings represents a user, and one of them is the FogBugz user. Instead of trying to guess which one, look for the long SID strings as these are normal Windows users, and make sure they also have their short and long date formats changed. After this, restart IIS for the change to take effect.
See here for more info.