Hello,
Are you not Migrating the Symantec Endpoint Protection Manager to the Symantec Endpoint Protection Manager 12.1 RU1??
Why are you importing the packages manually??
Could you let us know if you were able to import the other Windows packages properly??
Cause: Incorrect source file specified
Solution: Specify the correct source directory for package build files when adding a new package. An agent source package cannot be the compiled .exe file or else when the application attempts to find the sylink.xml file it will generate errors.
The correct agent source must be the full agent package either from the install CD or exported previously from the Management Server.