When faced with a remote class name, rmic attempts to convert it to Latin-1
using the Unicode escape mechanism defined in the main CORBA spec. See CORBA formal 01-02-01 3.2.5.2 Character Literals.

The format is \uhhhh where hhhh is hex value of the unicode literal.

However, rmic is using a capital U.

See the code in

com/sun/corba/se/internal/util/RepositoryId

There are two locations where \\U is used instead of \\u, both having to do with converting to and from Latin-1. Also look in the rmic -iiop -idl IDLNames and IDLGenerator code for capital U specific code.