Could you please send us your .muse file at muse-support@adobe.com along with a link to this thread? We'll repair and return it. If the file is larger than 20Mb you can use a service like Adobe SendNow, Dropbox, WeTransfer, etc. Thanks.
FWIW, the bug that caused this error within your file has been fixed for the release of Muse.
Sorry for the inconvenience.