This problem occurs after mission end and before the debrief screen.  What happens is your screen turns black and you are left with a egg timer.   You must CTRL-ATL-DEL to get out of it.

The cause of this problem is a file called 'Debrief.dat'.  It's located in  your main RedBaron3d folder.  Find this file and delete it.  This file is created when a mission DTD's in the middle of a flight, or you abruptly end RedBaron without properly finishing it the way it's designed to finish ie: hit esc and choose option.

Once this file is deleted from the folder, the problem will be solved.   

The Debrief.dat file is created at the end of the mission and is used to provide temporary data for Red Baron to display maps, kills, flight paths etc, directly after mission ends.  This file is then deleted by Red Baron and the game continues on to the next screen.  If this file is empty, as it will be if RB is abruptly ended, the debrief screen will not load, giving you the blank screen.

Again, simply delete the file.

DeltaK: "IMHO debrief.dat is normally a temporary file containing the necessary info/record for the after mission debriefing. When you click "done" on the blackboard after the debriefing, it is normally being deleted. When a mission ends prematurely due to CTD or freeze you do not go through the deletion process and the corrupted debrief-file remains in the RB-folder and has a negative impact on the next mission.

Consequently always delete debrief.dat after a mission crash/freeze"

Also... 

Skidmark: ""DEBRIEF.DAT contains the same info that would have been used for a video REPLAY function which Red Baron 1 had. A long missoin can produce quite a large file. If RB abnormally terminates during a flight, the truncated file resides in the RBII/3D main folder and can sometimes cause several problems including the blackscreen freeze. In one case, I got a repeat debrief; the same debrief ran even after running later missions. I usually don't bother going to the trouble of manually DELETING debrief.dat UNLESS it causes a problem.
CM11 NOTE: After the end-flight DEBRIEF and while still in-game, you can ALT-TAB, open CM11 and use it's DEBRIEF button to review the events of the flight for additional debrief info. Some parts of CM11's DEBRIEF function were never finished. You can also make a text comment log about the mission to save for future reference. One of those few cases where you use CM11 and RB MUST BE RUNNING. If you have CM11 you can read it's HELP file about this function which is explained in greater detail."