From the Solutions Enabler 7.6 security guide:  Hardware-based access ID: By default, a host's access ID is derived from hardware characteristics of that host. On x86 (32-bit Intel), x86_64 (64-bit Intel/AMD), and IA 64 platforms, a network interface MAC address is used. On other platforms, different characteristics of the host, such as a processor identifier, are used.  I've seen it change based upon new hardware added or even kernel changes, as it then discovers the hardware in a different order (specifically the network card order).  To guarantee the unique ACL key won't vary because of some some arbitrary hardware change or order of discovery, use "SYMAPI_ALTERNATE_ACCESS_ID = ENABLE" in the ../config/options file.  It will change it from what it currently is, but this key is then stored in an encrypted file rather than basing it on the hardware. 
Hi,  Can somone help me to know what factors causes change in sym ACl unique key.  Also is there way to make it consistent across upgrades (SE, OS) ?   Many Thanks, Viivek Jaiswal
change in ACL key