If the path in the error is from your development machine it means that there were unprocessed rows in the mp_IndexingQueue table before moving the site and database to production or else you are connecting to the production database and editing content from your development machine (which would be a bad idea).
To solve the problem, do this in SQL query analyzer
TRUNCATE TABLE mp_IndexingQueue
TRUNCATE TABLE mp_TaskQueue
to remove alll data from those tables
Then rebuild the search index on the production site
These errors could not be the cuase of errors that the user sees in the web browser because the indexing code runs on a background thread not on a thread that handles web page requests. So there must be some other problem that your users are reporting.
Hope that helps,