When we've had this error, usually it's a DLL dependency problem, not the AkSoundEngine.DLL itself.
For release and profile versions of AkSoundEngine.DLL, you need the Direct X end-user runtime 9.0c or newer, which provides MSVCR90.DLL and XINPUT*.DLL.
For the debug version, you need MSVCRT90D.DLL, which is distributed with Visual Studio.
You might be able to figure out which DLL is missing with http://www.dependencywalker.com/, note that this will report certain false positives.