Вы можете использовать метод Buffer.BlockCopy :
byte[,] bData = (byte[,])objTransLog;
byte[] baData = new byte[bData.Length];
Buffer.BlockCopy(bData, 0, baData, 0, bData.Length);
Пример:
byte[,] bData = new byte[4, 3]
{
{ 1, 2, 3 },
{ 4, 5, 6 },
{ 7, 8, 9 },
{ 10, 11, 12 }
};
byte[] baData = new byte[bData.Length];
Buffer.BlockCopy(bData, 0, baData, 0, bData.Length);
// baData == { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 }