Hi pranjith,
I'm using SnapCenter 4.0 P3.
I will give it a go using "-EmailPreference ON_ERROR_OR_WARNING".
If this works, looks like another error in the documentation. The SC 4.0 cmdlet reference (link) only lists the the possible values as " Always, Never, OnError, OnErrorOrWarning." without the underscores, none of the examples use the -emailpreference parameter either.
I will report back after further testing.