This issue has happened to me once and my friend multiple times (in the ~3 hours that we played together):

Inability to exit the game, disconnect, or return to space center - the only way to leave appears to be alt-f4.

Nothing in particular seems to trigger it - all of the times we were just playing around in orbit, pretty close together I suppose. One time, I was at the space center and he was in orbit and couldn't leave. The other times, we were next to each other in orbit.

We are still able to fly our ships and whatnot...so the game is not "freezing". But you just can't leave :S

Wonder what could be causing this!

Had this issue today when testing. with two copies of KSP on the same PC as the server. Crashed two Aeris 3A into each other while rolling down the runway. One of the users wasn't able to get out of the end flight screen, clicking any button to revert or space center had no effect.

Process: Basically sent one plane down runway at minimal throttle and ran 2nd one into it at full throttle from behind while still on runway. (don't ask why, I was just testing to see if collisions between players worked)

KSP/KSP_Data/output_log.txt for both users have been loaded to below link.

https://www.dropbox.com/sh/wy50v34g9ryezbs/AAC8ueun5Hd9o2n-IMWWMBRLa

Added a 2nd round of output log files. Was trying to replicate the issue. I cleanered the log file and tried again. Process worked fine on the first two attempts with both users being able to return to Space Center.

On the third I got the issue again with the user "Wile1411" craft being destroyed and spectating user "Player". "Player" later crashed the plane into ground with everything destroyed. Existed to Space Center no probs. "Wile1411" was spectating and saw two "ghost copies of "Players" plane crashed on runway. As "Player" had left scene to Space Center, "Wile1411" now had control on a cockpit and tank. (apparent left over from crash.) About 3mtrs behind this was a 2nd Aeris 3A with about 25% missing (1xwing, engine) but couldn't be switched to.
From "Players" POV, all was destroyed.
From "Wile1411" POV, the update from still alive to nothing seems to have been missed and there was a cockpit that became available to control after "Player" left scene.

Think the issue is the spectator is not processing / getting the message that a craft was destroyed and is still spectating debris that shouldn't be there. The user that has the last remaining craft existed fine after cockpit was destroyed.

The user Wile1411 spectating couldn't exit from the end flight screen or return to space center. Only working option was to resume flight.

Here's a pastebin that includes this issue:
http://pastebin.com/zZrdCjkR

Scenario: Crew Launcher by @randomkerman was trying to dock with my vessel, the Dock Chaser Core I. As he approached, I went EVA as Calnard Kerman. Later, random's game thought the station deorbited, so he left. I had Crew Launcher as the target, and got back in the Dock Chaser station.

Problems/symptoms: I attempted to exit to the Space Center, but the button was non-functional. Space Center button presses coincide with the NullReferenceExceptions on scene change in the log. Shortly after, Crew Launcher, which was only 800m away, disappeared completely from my game. In the ship map view, I could not see Crew Launcher or my own ship:

http://i.imgur.com/CKdWu2P.png

Both Crew Launcher and my (active and working) ship's orbits were visible, and Crew Launcher's orbit seemed to still be highlighted like a targeted ship. I could target and untarget other ships, but the Crew Launcher highlighted orbit never went away. I could not change to space center, or see my own ship on the ship map. Very weird.

P.S. Another shot showing the differing apoapses of the ghost ships. Note that my ship should have an icon visible right in the center of the screen:

http://imgur.com/EATXVme

I was able to burn my engine and affect my own orbit.

P.P.S. At the same time, unable to revert to launch or revert to VAB:

http://pastebin.com/R8JDp2xf

Continued - Clicking DMP disconnect button resulted in this log and the whole DMP UI disappearing. Now totally stuck and much kill the game:

http://pastebin.com/bUV34KMF

I've found a few problems got fixed by updating KSP, this is mentioned in the common issues. Can anyone confirm if updating your KSP version helps?

http://forum.kerbalspaceprogram.com/threads/77327-FAQ-0-23-5-Common-Problems-Crashes-Decouplers-EVA-Career-Saves-Game-Wont-Start

I've pretty much consistently ran into this after crashing the active vessel. This bug is quite annoying, but it's been thrown by KSP - So it's not yet clear what DMP is doing wrong.

The current workaround to this is SceneJumper, but it's a pretty lame solution - We'll need to find out how we are breaking KSP.

I believe SceneJumper doesn't work - This bug fully breaks KSP :(

Hmmm. Apparently, after hard quitting KSP, if you rejoin the server with a different name, the bug won't occur immediately (as usually when one gets the bug once, it stays with them on the server).

Are you guys running mods?

Nope, we're trying to have a clean test at first without any mods.

Inability to exit the game makes this bug high priority - if possible, can you uopload KSP/KSP_Data/output_log.txt to something like pastebin and link it here?

Today we played for a bit over an hour and did not have this particular issue - but here is the file (I just dropped it on my server) http://eugk.com/output_log.txt. I'm not sure if this file will contain the log that you need though; from the time we were having that issue, we updated to your latest build and thus far it has not happened...maybe magic fixed? :)

Keep up the good work!

DMP wants you to keep playing :D

In all seriousness - this bug is as big as the space center bug is for KMP (DMP shouldn't be breaking things). If you run into it upload the log. But you will need to run into it first :-/.

I'll check to see if that log file contains any hints when I'm able to.

http://pastebin.com/u1qQ4buT This is the KSP.log. Note the NRE's after trying to change scenes. There was a lot of debris around at the time. We were playing with rovers. haha.

https://www.dropbox.com/s/43djicsjp2zjqdp/dmpserver%202014-05-21%2013-43-17.log

This is the server log. I don't see anything in it that was strange. Maybe you'll see something I don't. Shrug. Hope this helps.

Or I might be wrong. There doesn't seem to be much of a difference, I was just lucky the first few times I tried

Closing this, It can definitely happen still, but the source of it is a NullReferenceException which seems to be thrown by KSP, which means this is a stock bug which is possibly caused by DMP.

If we come up with reproduction steps, I'll reopen this. From memory it only happens when a vessel or part crashes.