When doing a database detach attach for a 2010 -> 2013 upgrade, this error appears in the upgrade log:
/sites/sitename/Lists/MyList' has a schema that is incompatible with this version of SharePoint.
This means that the list has columns that are beyond the limits of SharePoint 2013. In my case, somebody created a test list with 256 columns of single line of text and some other columns. SharePoint 2013 has a limit of 8,000 bytes per row (item). Here is an interesting article about the limits and space that different columns take up in SharePoint: http://sharepointdirect.blogspot.com/2012/05/capacity-management-column-limits.html
Since mine was a test list with no items, I just deleted the entire list. If this had contained information, I would have had to work with the user to decide which columns could be deleted before the site could be upgraded.