It sounds like you have the same problem that I had when I installed FMSA v11. There's most likely a problem with the Apache httpd.conf file that wasn’t cleaned up by the FMSA 11 installer. I had to comment out or delete the offending lines then I was able to the Apache web server deployed successfully after that. Check your Console.app for any log/error reports for Apache which will hopefully point you in the right direction.
This link also has some details which might be applicable: