I got a similar error when using the new retarget animation feature in UE 5.4.
I found that if there is an array in the “animation track names” of the source anim sequence, and the array length is >= target skeleton bones, this crash will occur. Adding virtual bones to the target skeleton before retargeting allows us to bypass this issue.
It’s important to note that the number of virtual bones added depends on the difference in quantity. For example, if the length exceeds the target skeleton by 5, then at least 5 virtual bones need to be added to the target skeleton.The hierarchy of the virtual bones are not important; they can be added to the root or any bones.
Remember to save and restart UE after adding virtual bones to ensure the new bones take effect before retargeting.
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