Please refer to the following document :
If the upgrade doesnt solve your problem try the following steps:
1)Confirm Data Execution Prevention is only monitoring Windows components.
Right click on my computer, go to properties.
Click on the advanced tab, and click settings under performance options.
Click the Data Execution Prevention, and set from All to only essential windows components.
The act of disabling this occurs during startup, so it is likely that the issue will occur right after the first reboot.
2)To fix the problem on a server, on unmanaged clients, or on a small number of managed clients
On the affected computer, delete the numbered virus definitions folders in the \Program Files\Common Files\Symantec Shared\VirusDefs folder
Restart the Symantec AntiVirus service.
To fix the problem on a large number of managed clients
On the parent server, download the latest .xdb file to the Symantec AntiVirus program folder.
For directions, read the "Copying an .xdb file" section in the document Updating virus definitions for Symantec AntiVirus Corporate Edition 10.x and Symantec Client Security 3.0.
On the parent server, delete the contents of the folder \Documents and Settings\All Users\Application Data\Symantec\Symantec AntiVirus Corporate Edition\7.5\I2_LDVP.VDB.
Do not delete the folder itself.
On the parent server, restart the Symantec AntiVirus service.
This action sends new virus definitions to the managed clients.