Data not showing up in .sav file

We ran a study with 4 subjects last night and experienced almost no problems with Medialab while they were filling out questionnaires. However, when we looked for their data, one person's did not show up even though we did everything correctly. Do you have an idea as to why this might have happened, or where their data might be? It's not in the text file either.
Also, another subject was using the computer and every once in a while medialab would not let us click the response and move to the next question (I don't think the computer froze because the cursor still moved). We restarted Medialab and it happened one more time, on a different question though. We restarted Medialab again and went through the questionnaire perfectly (this person's data did show up). Have you heard of anyone else having this problem before?
Thanks

Are the experiment files located on a network hard drive or are there copies on each local machine? Are you saving your data to a common network folder? If running over a network or saving data over the network, are you using "unique machine values" to identify the different machines for data writing?