After running fine for a couple of weeks, Broken Link Checker just started putting up this message in a pink box on all the pages visible to logged in users (not just plugin pages, and not just users with admin permissions either).
"Broken Link Checker installation failed. Try deactivating and then reactivating the plugin."
With a highly detailed report of where errors creeped up. Deactivated, then reactivated. Problem recurred within 2 hours.
There are threads related to this problem on multi-site blog, but this is a single installation running a Woo Theme and
Strange thing is trying to figure out what provoked this. No recent updates to core or plugins or theme. Not even any new broken links.