"This Person Is Busy" seems quite common. Probably CPU related because of sheer # of scripts Enderal uses.
Dialogue-- esp. if NPC is moving from one place to another, and has animation-- paces floor, looks at map, rubs chin... tends to get the "Person is busy" thing.
Give whatever it's supposed to be doing in the background time finish. If 5-10 minutes still "busy" - try exiting cell, going back in, rinse & repeat.
If that doesn't work, can console stages, but (for me at least) dialogue always worked for MQ, just very slow sometimes.
Best wishes & post back if still stuck. : )