Welp buddy, then you’re outta luck. I’ve asked you to make sure that the other actor is derived from the block class and you said it was. There are very few reasons that a C-style cast will fail and under the hood, thats all a blueprint cast is. Therefor, without being able to shift through the problem…I can’t help you and I doubt many other people can. It is asking us to solve a problem with a missing piece.
For the record, all cast types will fail if the other blueprint is not derived from the block blueprint. That is also about the only reason any cast “would” fail unless this is a bug, but that is doubtful as I haven’t seen a cast bug in ages and it would affect all cast considering they’re derived from the same logic.