Have you spoken with
Coinbox1, the casinos' forum representative? He may or may not want to be of help.
I asked about this issue to TrustDice representative and he has given a response in their ANN thread today.
The game provider has given us a very broad response, which we have provided to the player. Unfortunately after analyzing our NDA restrictions in our contract with them, we found that we are not permitted to disclose it in a public forum. Overall, we neither have a clear idea why the game provider thinks it was necessary to rejected the bet.
But after reading the player's descriptions of their behaviors, my personal observation is the same as yours. Since they have placed opposite bets in the same round of the same game with the same provider at only different online casinos, it could be easily detected by the game provider as fraudulent and collusive behavior, therefore getting the bet voided. It looks like player collusion being found.
Based on their statement, the game provider has rejected the bet. But they haven't told the exact reason of rejecting the bet to TrustDice team. They have forwarded the game provider response to the OP. He should reach the game provider to know the exact reason.
~snip~
TrustDice team suggested you to play the Dice or Crash game which has 1.5% house edge. You could easily complete the rollover requirements of your deposited amount by using wagering strategies in those games. I'm wondering why you took risk and placed a $500 bet in Baccarat game! Did your friend also placed $500 bet on the opposite hand in other casino?