The lack of a complete flight sounds like it might be related to how the flight is triggered to end. Is your FSFS system set to end the flight when the brakes are set (please check it)?

If you think you've found the problem and solved it, do a very short flight to check it. Just put a small plane on a long runway, start FSFS, take off and fly for at least 30 seconds and then land on the same runway and make sure you get your log book entry.

Also - forgetting to load a flight plan into FSFS is not a problem until you land at a nonILS airport or if you want the points for passing waypoints correctly and in the right order.

If you forget to load it, just load it as soon as you remember to do so in your flight. You will not get full points for passing waypoints if you have already missed some but you will get the right NonILS data in place which is essential for non ILS landings AND you will get some points for passing the waypoints which remain.

 Transferred reply!

SL:

As I said. It´s me! I have my FSFS system set at "stopped and brake set". Problem in the first attempt was that MsA didn´t say anything when I stopped. She normally evaluates the touchdown, (and never spares my feelings either) but this time she said NOTHING. But never mind. There are always incidents in computergaming (and in computers in general) that make no sense at all.

You weren't arguing with her were you? That is guaranteed to produce long periods of silence, believe me...

On the second attempt, I don´t know how I got the flight plan thrown out. Might have forgotten a disconnection and reconnection, and thereby lost the flightplan, but why does the flightplan dissapear when you disconnect? Coulden´t it remember the last flightplan?

The idea in FSFS is that if you disconnect from FS yourself, or are disconnected by FSFS as the flight can no longer continue (due for example to the pilot changing the aircraft) then all data is reset.
The slate is wiped clean. The decks are cleared. Nothing left. Not a sausage. Zilch. 

This is done by design, that is, intentionally, as otherwise a somewhat messy situation could result.

Anyway, I did what you suggested, loaded the Cessna 172 on the longest runway I could find, and took off, flew for more than 30 seconds, and landed. Did it twice, and got a logbook entry both times. So everything works, just as I thought it would. I simply fu.... up on my two flights. I´ll have to do it a third time, and do it properly!

Splendid! Good to hear that FSFS is in the clear!