I had one webpart that displayed error after site migration to SharePoint 2010:
Unable to display this Web Part. To troubleshoot the problem, open this Web page in a Microsoft SharePoint Foundation-compatible HTML editor such as Microsoft SharePoint Designer. If the problem persists, contact your Web server administrator.
I checked webpart properties and noticed:
- Query was configured to take one list
- There was grouping applied – grouped by Site
SharePoint 2007 was working fine even grouping was quite silly as all elements were coming from one site only, due to query scope.
In order to fix this problem, you need to change scope of the query to ‘site collection’ or ‘subsite’ and then filter content type or list template. Then option to group by site will be available again. If you scope it to lsit or library, ‘site’ is not available to choose.