Was I supposed to be able to make this castling move?

I'm playing chess v. the computer; was I supposed to be able to do this?

[Site "Chess.com"]
[Date "2015.06.05"]
[White "Player"]
[Black "Computer - Expert"]
 1. b3 b5 2. Bb2 Nf6 3. a4 bxa4 4. bxa4 e6 5. Ba3 Be7 6. Qc1 c5 7. f3 d5 8. e3 Nbd7 9. Bb5 O-O 10. Bxd7 Qxd7 11. a5 Qc7 12. a6 e5 13. Bb2 Rb8 14. Bxe5 Qxe5 15. Nc3 d4 16. Nb5 Rxb5 17. Qa3 Rb6 18. O-O-O dxe3

Yes you can castle here. In this link will tell you about castling, just scoll down to 'castling'.

http://www.chess.com/learn-how-to-play-chess

This link here tell how to post your game....

http://www.chess.com/forum/view/help-support/a-guide-to-posting-your-games-on-chesscom

Thanks for the tip.

In that game you were able to castled which was fine. 

Ok, I see now; I thought that since the black rook in square b6 could attack b1, that this meant I couldn't castle this way.  Since my king wasn't passing through b1, it's a legal move.

That's right.