my challenges disappear!

In the online chess section (the "correspondence based" just to be clear) when I try to start a new challenge and nobody accepts it it disappear after few minutes.

Several times I tried to make a new challenge with a certain starting position, it remains up there only for a couple of minutes. Somebody was able to accept one, but as it may take a while to find somebody willing to play from a certain position, the fact that the challenge does not stay up is really annoying.

Can somebody shed a light on this?

thanks

I know just that you can have (10 - MyMove!) challenges.

Umm, do you understand?

no, what do you mean?

If you have 4 games "to move", so there is a sign "My Move!", you can make just 6 challenges. If one of your opponents move in that time (you have 5 MyMove! signs), then one challenge is deleted.