Animation Length Limit
From Second Life Wiki
Animations can have no more than 60 seconds worth of unique frames.
Linear animations will therefore end in 60 seconds or less.
Looped animations will only end when stopped.
A bug causes the reference frame in the BVH file to be included when measuring the duration of the animation, even though it's never displayed (see VWR-27044). That means the real length limit is less than 60 seconds. How much less depends on the BVH file's frame rate, since you have to shorten a 60 second animation by 1 frame.