I upgrade the sep client from 11.0.7300.1294 to 12.1.4100.4126 by use install over old version but it roll back and fail !! So, I try to uninstall by use clean wipe but it still fails ! please help me to solve it. 

This problem occurred only Windows XP SP3 and Windows Server 2003 R2 SP2.

Thanks.

Post the SEP_INST.log file and SIS_INST.log files.

Refer to this article:

What logs do I need to gather in order to troubleshoot a failed SEP 12.1 client installation?

The other thing you can try to do is install the unmanaged version from the download ISO to see if it will install. If it does, you can replace the sylink to make it managed.

Can you post sep_inst.log ?

See this thread if help you

https://www-secure.symantec.com/connect/forums/can-ru4-mp2-client-be-upgraded-directly-121-ru4

SEP_INST.LOG 

Attachment(s)

SEP_INST.LOG__2.zip   183 KB 1 version

I try to install 12.1.4104.4130 - 12.1 RU4 MP1a over 11.0.7300.1294 but it's failed aswell. 

Please help me to solve it.

Thanks.

have you try attached thread solution ?

https://www-secure.symantec.com/connect/forums/can-ru4-mp2-client-be-upgraded-directly-121-ru4

You can install the unmanage package on failure client.

After install replace sylink.

Thanks @chin_aust i will try ! 

Now, I try to fresh install the OS and install the SEP client again, the result as fails.

I suggest you can raised support ticket i think some think Bug in SEP 11.x to SEP 12.1.4100.4126 Upgradtion.

We have received multiple thread same problem.

Some other thread

https://www-secure.symantec.com/connect/forums/upgrade-deployment-fail

https://www-secure.symantec.com/connect/forums/failure-upgrade-sep-11-12

https://www-secure.symantec.com/connect/forums/endpoint-deployment-roll-back-while-installing

See the article

Symantec Endpoint Protection 12.1 client install rolls back, returning 1603

If above not be work then run the cleanwipe tool, similar logs error in below attach thread

https://www-secure.symantec.com/connect/forums/endpoint-installation-error

Cleanwipe tool is avaialble in fileconnect at tool setup.

Remove the previous version with cleanwipe and try a new fresh install

Dear All,

Now I can solved this problem !!

This problem occurred from Windows Root Cert is not up to date then I update Windows KB931125.

I can install the SEP client successfull.

Thanks.