We should log more details for wiki rendering errors during indexing, and should recover from this specific error (e.g., removing the illegal URL); I'll open issues for these.

In the mean time, the easiest way to find this wiki is to search for the errant pattern in the wiki body, executing something like this PostgreSQL query:

  SELECT * FROM comm.PagesAndVersions WHERE Body LIKE '%=c%'

If you don't have direct access to the database, you can define a temporary external schema pointed at the comm schema (with a unique name, so it doesn't interfere with the built-in one) and then use a normal contains filter on the body column. You will need to define the external schema high enough in your folder hierarchy and apply a folder filter to the wiki-containing folders.

Adam