The dispute has its roots in the recent agreement between NYRA and TVG, granting TVG additional exclusivity rights with respect to account wagering. As I understand it, the tracks can still offer the signal as simulcast centers, but their right to offer account wagering is limited, and they're boycotting the NYRA signal in protest. Here's a link to a Lowell Sun article (you'll also get pop-ups) with more details:

http://www.lowellsun.com/Stories/0,1413,105~4767~2408784,00.html