I've also encountered the same problem which you described, i.e. unable to login with TWS 854.4 / Java 1.5.0_04 (tried it quickly on the "experiments" PC last week and thought I'd debug things later). Which is why I remained with TWS 853.8 and 851.9 for my regular trading, until this happened today and I had to try every possible TWS/Java/OS combination in a very short time. I also tried login with 854.4 but in a DIFFERENT account, which worked, so I thought (mistakenly) that it was a TWS version issue. As Xenia pointed out, this particular issue had nothing to do with TWS/Java/etc version, but with IB itself. So I had to wait for IB to fix it from its side. PS: IB has fixed this issue for my account (error report ticket 08:38EST and fix 10:10EST).