You are trying to install the Symantec Endpoint Protection Manager (SEPM) and a message similar to "Error 1406. Could not write value. . ." appears, referring to specific registry keys or values:
Note : Write value appearing int he error message may differ. Eg. "Error 1406. Could not write value DebugLevel......"
Server to which SEPM is being installed and already has the Symantec Endpoint Protection (SEP) agent installed.
Tamper Protection is blocking access to that section of the registry.
If you have Tamper Protection unlocked for this agent, you can simply disable it in the user interface (UI).
If Tamper Protection is locked and this is your only SEPM, you must uninstall the SEP agent prior to installing SEPM.
If that does not resolve the issue, then either your account does not have permission to access these registry keys/values or some other security software is preventing access.