There is a known localization issue with the current Spatial Metadata GUI's v1.1 release's handling of textfield based number entry in the GUI for users in select regions with non "English US" region settings enabled in their OS. Dev efforts are underway now to solve this. :)

At the moment, you need to set your computer's localization settings to allow a period based separator to be used for the decimal point mark. If you have your number input preferences in your operating system set to use a comma value for the decimal point character there will be an error.

Summary: The GUI wrapper tool is a thin shell that is passing data to the Spatial CLI tool through the command line interface. A North American localized number input setting has to be used until the next dot update is shipped. (Sorry about that!)