Report Commander exports to a temporary file (which is the file name that you're seeing in the log) and then renames the file to the final name. It's the rename that's failing. The reason is that the ${now} variable formats the date/time with colons, which aren't valid in a file name, so it fails with the "The given path's format is not supported" error.

To avoid this, use the now function instead of the now variable, and specify a format that doesn't contain invalid characters for a file name. For example,

@now("yyyy-MM-dd HH-mm-ss")