Hello, For the past couple of weeks, since downloading 6.4.2, I've been running into occasion panics: ghc-6.4.2: panic! (the `impossible' happened, GHC version 6.4.2): tcIfaceTyVar a{tv} Consistently, changing certain files causes this error. Which files in particular cause it vary by machine - unfortunately, I don't have a very wide variety of machines to test it on. My concern is that this is occuring in about 5000 lines of proprietary code, and I'm not sure where to start in trying to create a repro case. Any guidance? Thanks. /g