You have 0.00148702 BTC in that account and are trying to send out 0.001 BTC. This would suffice were it not for the transaction fee of 0.0005.
Thanks
I understood from reading something somewhere (I'm quite new and I can not remember where I read everything) that transactions can be made without fees, and they just will delay more than if made with fees. Am I wrong?
That's correct in theory. However bitcoin-qt enforces a mandatory "voluntary fee" of 0.0005 for a transaction. You'd need to use another client to avoid that.
Looks like gyrsur has bumped your balance up to the necessary amount.