In Mac OS 10.8 a GateKeeper feature was added which warns about installing apps that didn't come from the Mac App Store:
To get the Mac USB driver to load you need to tell Mac OS to trust that file:
1. Right-click (or control-click) on FTDIUSBSerialDriver_10_4_10_5_10_6_10_7.mpkg
2. Click the Open button.
For more info, see http://osxdaily.com/2012/07/27/app-cant-be-opened-because-it-is-from-an-unidentified-developer/
If you are getting this error when opening vmAIS, you need to do the same thing to disable the GateKeeper warning message.