I've successfully run the 2014 upgrade advisor in QA ( on a two node cluster housing four instances ) after installing the sql script DOM and upgrade advisor.
In production, also a two-node cluster, I've tried various combinations of server/instance and it does populate the database names, but when run throws the "network path not found mscorlib" error. Tried the sql server virtual name ( short and fully qualified ) and also the name of the physical server, using "MSSQLSERVER" as the instance since I want to test the default instance first.
Tried installing the x86 version of script DOM, no help. Ran Advisor as admin, no help. These are Serve 2008 R2 64-bit servers running sql 2012 Enterprise 64 bit and I'm doing all my work right on the server. I'm a local admin and sql sysadmin on there.