many, many times…

you can use the two together, but in the w3 total cache configurations, for each type of caching in use, you must disable it on the wp page you have the forum displayed on…  each w3tc caching type as a way to exclude pages…

since all the forum content displays on that single wp page,  you cannot cache it…  the caching plugins assume that page is static, but its not, so it will get it wrong…  the appearance of many forum pages is just an illusion using url rewrite black magic…  its still all being displayed on the single wp page… so attempts to cache it will not get the correct data…