After installing Symantec Encryption Desktop on OS X and performing the initial reboot, the prohibitory symbol appears (a circle with a line through it). At this point your only option is to reinstall the OS.
Re-purposing Mac systems that have been previously encrypted with Symantec Drive Encryption or Apple FileVault encryption.
If a Mac system has been encrypted with either Apple FileVault encryption, or Symantec Drive Encryption (formerly known as PGP Whole Disk Encryption), it is necessary to completely wipe out the partitions and start from scratch if decryption has not been performed. In some very rare circumstances, some Mac systems that have been decrypted, have not properly uninstrumented, leaving behind remnants of the instrumentation or boot markings. When this has occured, and a system is re-purposed, boot issues may occur. The boot issues may not occur immediately after encryption occurs, and may occur after a Mac OS update.
This is an issue that can occur if the markings on the disk are not completely cleaned after a system has been re-imaged. In most cases, decrypting a system fully, and confirming the system is no longer encrypted will ensure a system will properly boot after Mac OS updates. If a system has been encrypted, but simply re-imaged, although the system may appear to operate normally, unexpected boot problems may occur.
If a system has been encrypted, either with Apple FileVault, and has been re-purposed, it is necessary to completely repartition the system before attempting to encrypt a system again with Symantec Drive Encryption. Using the normal Mac OS X installation process, before proceeding to install the OS, use Disk Utility and re-partition the system. It is recommended to create multiple partitions on the drive, click apply, then reset back to 1 partition. This will ensure a thorough repartitioning has occured and will ensure all previous markings on the disk will have been removed.
Alternatively, using fdisk, or a third-party utility such as DBAN to completely wipe out the partitions and then doing a repartition during the installation should also clear this out. Ensure the partitions are completely wiped/destroyed, and are recreated from scratch. Once this has occured, a reinstall of the OS would then be possible.
An example of fdisk that has been observed to clean off previous partitions is below:
fdisk -u /dev/disk0
WARNING: Only perform these operations on disks that you intend on re-installing the Mac operating system as this will remove all partition data from the system.