Hey there @Hamo! This is a weird one. Which version of UE4 were you using? I’m guessing 4.27 but don’t want to assume. That specific line is crashing due to a check on the tag. Which seems descriptive, but in reality it isn’t. Errors like this on stable engine versions are often down to interference with a plugin or accidentally messing with engine content in project. This only occurs during BP compilation though?