The post contains instructions on how to create a file called fs2_open.log using the debug version of FSO. The last post is extremely important if you are experiencing a problem that isn't included in this thread. The next four posts contain descriptions and solutions to those categorized problems.
The first post contains some useful general tips on what to do with different kinds of problems, as well as a list of the most common known problems, categorized under "General Issues", "Graphical Issues", "Sound Issues" and "Gameplay Issues". Not to mention that it is really a lot faster if you read through this thread, find a solution and apply it compared to you asking about your problem and waiting for someone to tell you the same things that are explained in this thread. Before doing anything else, read through this thread! In 9 cases out of 10, the problem/error you've encountered is a known issue and has already been answered here. This is the FreeSpace troubleshooting FAQ.