Message Oracle PGA-21014 - invalid character(s) found in network name string

ERRORinvalid character(s) found in network name string
CAUSEOne or more invalid characters were found in the network name portion of the fully-qualified local LU name.
ACTIONThe network name must begin with an upper-case alphabetic character or one of the national characters $, #, or @. Subsequent characters can be upper-case alphabetic, national, or numeric. Reenter the command line with a valid network name specified in the fully-qualified local LU name.