Grant's Army Stack with Strength of nearly 3000 is blocked from moving from a region with 100% Union MC through a region with 100% CS MC on his way to Natchitoches.
I got this message in the Mail Box:
Selecting Grant's stack shows that the region between Harrison LA and Natchetoches TX is marked red:
There are 3 CS leaders without any troops in the region, one of which is John Bell Hood with Corp status, who had his last couple of units destroyed a couple of turns previous. The only other CS unit anywhere nearby is Standwatti with troops at just over 50 strength and far enough that I don't think they could have played a role in this.