[ic] Issue with upgrade to 5.10

[DB]

I tested upgrading to 5.10 on my dev machine. Things mostly work, but
I'm having some issues with the Solr stuff that Racke helped me set up.
If I revert to 5.8.2, things again work.

If I try a solr search under 5.10, I see on the browser:
Sorry, there was an error in processing this form action. Please report
the error or try again later. (Can't locate object method "new" via
package "Interchange::Search::Solr" (perhaps you forgot to load
"Interchange::Search::Solr"?) at (eval 793) line 7. )

and in the catalog error log, stuff like:
[06/February/2016:20:51:49 +0000] SOLR /cgi-bin/SOLR/ajaxsearch.html
Missing: ajaxsearch.

Any thoughts why the custom code would stop working on 5.10?

DB