The normal process for removing Symantec Protection for SharePoint Severs 5.1 is not working.  

Steps to uninstall 5.1 Manually

1. Registry „HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions“ remove the sub key „AVScanner“
2. Run IISReset to Restart SharePoint Server
3. Stop the Service „Symantec Protection 5.1.5 for SharePoint Servers“
4. Run Installutil.exe on the „Symantec.SharePoint.Service.exe“ file.
    Sample: "%SystemRoot%\Microsoft.NET\Framework\v2.0.50727\InstallUtil.exe" /u "%ProgramFiles%\Symantec\SharePoint\Symantec.SharePoint.Service.exe"
    For more information „http://msdn.microsoft.com/de-de/library/50614e95(v=vs.80).aspx“
    This will unistall the Service.
    Alternate you can delete the Registry Key „HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SymantecSharePointScan“ and Reboot.
5. Delete the Folders.
    By default „"%ProgramFiles%\Symantec\SharePoint“ and „%CommonProgramFiles %\Symantec Shared\SharePointEngine“