2010 Experience Search Web Part unable to display

Question

I have a SharePoint 2013 farm with a couple legacy site collections running in 2010 Experience mode.

Search works fine for the 2013 sites, and search successfully crawls all sites.

When I try to use search on the 2010 sites, I get:

"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 have gone through everything I can think of.

1. Cloned the site and upgraded the clone to 2013 (search works)
2. created a new 2010 expierence site collection, the problem persisted.
3. applied all CU's up to October 26'th
4. Changed the master pages.
5. Deleted and rebuilt the search application
6. Double checked database permissions on the SQL Server

At this point I'm at a loss, and I cant find anything about it.

Answer 1

In a few instances of upgrading to 2013 I have encountered similar issues with a 2010 search center not working on a 2013 farm. In these instances, we have either gone forward with the upgrade of the site collection -OR- created a new search center in a 2013 site collection and configure the 2010 site collection to use that search center instead of the 2010 one. I know this really isn't a solution to making the 2010 search center work, but it does offer a workaround to getting your users searching.