Since Collaborator uses the Subversion command-line client and its native commands to fetch the data from the local SVN repository or the SVN server, Collaborator will abort the entire uploading process if at least one of the outputs of the native commands will be unexpected or contain an error. This is done to prevent losing data or uploading the incorrect files to the Collaborator server.
It would be good if CodeCollaborator would be able to handle importing a review from which a file has been removed during a merge to handle this differently. i.e: continue to import the files it could parse, and maybe put up a warning or something, rather than aborting the import.