HI, 
  
I installed Forge 9.11.1.916 on my Mac OSX 10.8.5 Minecraft 1..6.4. 
The client installation worked perfectly including 2 library files. 
When I opened Minecraft with profile Forge appeared an owfull message "Forge Mod Loader has found a problem whith your Minecraft intallation. The mods and versions listed bellow could not be found: KeithyUtils:[1,1,]. The file "ForgeModLoader-client-0.log" contains more information". 
I opened that file but I understand nothing. 
I deleted twice Minecraft and Forge and re-installed with the same problem. 
¿May someone help me? 
  
Thanks, regards and good life, 
Jorge/Buenos Aires/Argentina