/www.richardsnotes.org/archives/2005/04/29/50mm-lens-contact-points/).
/www.lensrentals.com/blog/2008/12/canons-error-99-the-man-the-myth See page 4 for a list of common causes of Error 99. Page 6 gives some things to try to correct the error.
/www.shutterbug.com/content/canon-eos-20d-error-99-problems