When both cMap and WP Flexible Map are installed on the same site the directory page using the cMap template will no longer function. The issue is usually caused by the Google Maps API being loaded on the page twice. cMap will load it only on its page in the page footer. Mapping plugins should do the same, but some, like WP Flexible Map, load it on every page regardless if there is a map or not. This of course causes the Google Maps API to be loaded on the cMap page twice which can break the API.
The solution is to use a mapping plugin which will load the Google Maps API only on its pages. One such plugin recommended by a user is Robo Maps.
NOTE: This FAQ was written based on WP Flexible Map 1.9.2