The best approach when getting the "unknown error" is to systemmatically exclude files, registry entries, ini files, and shortcuts to determine what item is causing the problem. Then this item can be modified in the Repackager view or by editting one of the text files created by Repackaging wizard.
An alternative is to just exclude the problemmatic entry and then build the ISM with Repackager. Then Editor can be used to edit the ISM to correctly add the excluded item before building a MSI.
-Ajay
