Hi,
Thank you for posting your query in Symantec community. I would be glad to assist you here.
Could you verify the sopho's version again. I see the list of supported versions except 10.3
Open the following link & go to Page-34 there you will find supported versions list.
https://symwisedownload.symantec.com/resources/sites/SYMWISE/content/live/SOLUTIONS/195000/TECH195029/en_US/Symantec%20Endpoint%20Protection%2012.1.5%20Third%20Party%20Security%20Software%20Removal%20Support%20List.pdf?__gda__=1449039183_6331da3c3aa722db8ac19718df7adb20
Also, did you select the following option under client install settings?
For any other unsupported product we do recommend Sepprep.tool.
SEPprep is an unsupported tool that is designed to uninstall any competitive product automatically. This tool can also launch another application before or after removing all competitive products.
Configure this tool to first remove all competitive products (including Norton products) and then launch the SEP installer automatically and silently.
http://www.symantec.com/docs/TECH148513