A warning in the output using new r15 animation custom character r15

Hi, i have a problem using the new r15 animation but I am making custom character that is r15 and I animated the animation but when I played the game it said this in the output:
Strafe blending disabled. Run and walk must be strafing-friendly.

Now I don’t know what that means
and the animation works but if u can explain to me.