The above error occurs for all connected clients apart from the client which launched the vessel causing this error.

This error exists as of commit e2409ba and with latest KSP (0.90.0.705 Beta).

I haven't managed to reproduce this error yet but I know about this one. Can I get a copy of the universe, dmpserversettings and a client log file?

Sure thing! Also includes server log.

https://www.dropbox.com/s/jazn9e8ueq0ziq9/Error%20handling%20VESSEL_PROTO%20message.zip?dl=0

Sorry about that - just checked on it. Where did you get this dev build from? - it looks like a custom compile.

"[0.5925589] DarkMultiPlayer: DarkMultiPlayer Custom, protocol 32 Initialized!", and as you have mod control disabled this should have been fixed in e0c4cc6

I compiled it myself from the source, I was using e2409ba at the time, which should include commit e0c4cc6

Problem still exist as of 07590d4 :)

Is compression enabled on your KSP client? And is it enabled on your server?

Compression is disabled server side, my client's servers.xml states the following:

Which I assume means that the client tries to use compression?

This seems to be solved as of c2c2131