There is an unpleasant bug with all versions at this time that will cause odd errors with groups. This was reported at AUGI and Autodesk has responded there as well as to support requests that they are working on the problem. The issue is related to code that is supposed to deal with leap years.
Keep an eye on the download pages at Autodesk as this is a serious enough bug that I believe a new build will made available as soon as possible. The temporary workaround suggest by Autodesk is to briefly change your pc's date to either February or the previous month to permit the feature(s) that isn't working to work. This has its own problems and you should carefully consider this before doing it.
Known Conditions that generate error "Unspecified Error".
Saving Groups out of a project
Save Detail View out of Project
Edit Group from Project Browser via Right Click (Edit Group on Options bar works)
Create new project choosing Template: None then attempt to choose Unit of Measure