There area few things that can cause this error. Resolving it can also depend on what version you are on, and if it is a managed (viaSymantec Encryption Management Server) or unmanged installation.
The machine UUID is a globally unique identifier that keeps track of that system when reporting to the management server. In earlier versions of the product it was assigned at installation. In the newest few versions, it is assigned when encryption begins.
If you are imaging systems with Symantec Encryption Desktop (SED) already installed, make sure you are on version 10.3.2 or later. If imaging with a prior version in a managed environment, you will need to contact support for assistance and follow this article:
http://www.symantec.com/docs/TECH214370
If you are not imaging, it is most likely an issue with the registry value not updating properly during installation or encrypion. This can often be caused by security software or antivirus programs preventing changes in the registry. Usually you can fix this by uninstalling, disabling any antivirus or security software, and reinstalling. You will also want to make sure neither of these are active when you begin encryption.
Let me know a few more specifics (version, managed/unmanaged, etc) and see if the uninstall/reinsall works for you.