I have the error:

You have too many open bids, your squad size will be over the limit.

i dont know what does it mean. Want to buy a goalkeeper because I have only one. I have 19 players in my team so my squad size wont be over the limit. I what can I do, only 2 hours left for bids.

Okay, I can see that player I want is still in youth center, thought that he is in first squad.

That's right
Academy Level 1 only holds a maximum of 3 youth players. You have 2.
You can only enter 1 auction for a 15-16 year old youth player.