Audio problem: When Xander, Willow and Ampata meet up at The Bronze, the song the band is playing is at the point of a guitar solo. If you watch Oz (who has already been established as 'lead guitarist') on stage in the background; he's blatantly NOT playing that solo. The hand movements don't match up.
Continuity mistake: When Buffy opened the trunk for the first time, the corpse of the real Ampata is lying with its head to the right of the trunk. When she opens it the second time, the corpse is lying with its head on the other side.
Plot hole: When Ampata is first released from her imprisonment, why didn't she break the seal then? She knew the only way to re-mummify her was to put the seal back together, so why not shatter it completely instead of leaving it in large fragments? (00:08:40)
Continuity mistake: Ampata tells Buffy she has no lipstick, but earlier that episode we saw her using lipstick, in the high school bathroom right before the bodyguard attacked her. (00:24:20 - 00:25:40)
Visible crew/equipment: When Ampata agrees to go to the dance with Xander and they walk off down the hall, a shoe can be seen in the bottom right of the screen within the last few frames stepping into shot.
Chosen answer: He had larangitis and because of the shooting specifications they had to have him shoot the scene with a bad throat, they then re-recorded his lines and dubbed them. At various points during the scene and indeed the episode you can see him touch his throat or rub it.