The SharePoint library is not visible in the 'Get Document Reference -Specify Library' step in the Workflow.

Before You Begin

The issue can possibly be caused by a Site Title rename.  K2 artifacts are generated and placed into a category name similar to the SharePoint Site title.  After the site title is renamed, the artifacts will be generated and placed in the category with the new site name.

How-to Steps

You can resolve the issue by renaming the Site back to the original name then recreating your library and SmartObject.