I used a good belgium chocolate, heavy cream, and corn syrup, and ganache is grainy. Any suggestions?? More corn syrup to smooth it out?? I had it in mixer for a long time. Thanks for any advice!!

it sounds to me like your chocolate seized, which is usually caused by water coming into contact with the chocolate. it doesn't take much for this to happen. was everything (bowl, utensils, measuring cups) completely dry? even the tiniest bit of water can cause seizing, including the steam from a double boiler.

when making ganache, i normally heat the cream (and corn syrup in the case you are describing), pour it in to another heatproof bowl, and then add my chocolate.

Actually you can get grainy ganache for a number of reasons, not just seizing. Overmixing can cause graininess. Not having the heavy cream hot enough, not letting it set. There is a whole slew of reasons.

It is difficult to have the chocolate seize up when making ganache given you are adding at least the same weight in liquid as the chocolate. It is when you are adding less that you have to worry about seizing. Possibly you did not pour it all in at once. To avoid this, next time add the chocolate to the cream instead of the cream to the chocolate. You will always guarantee to have more liquid in weight than the chocolate.

Take the ganache and heat it in the microwave in 30 second increments and stir. Eventually it will get warm enough where you can stir it and see the graininess disappear. Then let it resit, the graininess should be gone. I have had success doing it this way before.