Make sure that you have the versionable aspect applied to your content. Items created/uploaded through Share will have the versionable aspect applied by default, but this is not necessarily the case when content is created via other inputs like WebDav. If you need everything in a particular area to be guaranteed to be versionable, use a rule at the top point in the folder/space structure that applies this aspect on creation of content (with the condition that it is a subclasses of cm:content)
Regards
Steven
