HellsGuard

Make sure that you're both updated to the same versions of KSP, as well as using the correct DMP version. I am fully updated on KSP and use the 942fbbb Dev version of DMP on my client and my server that has 6 of my friends on it and I have no issues. You're using the updater so it is probably not grabbing the dev version that you need if you're fully updated on KSP.