You should install the 32 bit C++ runtimes, even on a 64 bit os, because these are 32 bit apps and requires 32 bit runtimes. However, our installers automatically install them so, the problem shouldn't normally happen, but it won't hurt trying this solution first.
Do you recall being asked the first time your run FSX, to authorize the Addon Manager to run ? If not, this might be an indication the program hasn't been installed, most likely because the antivirus has blocked it.