Hi ska234 - thanks for posting the file!

So I think what you're running into is trying to use 2 cutting curves that happen to touch each other at a shared endpoint. The booleans will try to automatically join together curves as a part of the boolean process and in your case here for example:



if those 2 cutting curves get joined together since they're on different planes the resulting joined curve is not on a single plane anymore and so does not know which direction it should be extruded in to form the cutting surfaces.

In case like that with 2 curves in different planes coming to a shared endpoint you will need to do the boolean in 2 passes, one for each individual curve rather than using both curves in the same single boolean operation.

Is that one of the things you're running into?

If it's not that and you're having a problem with one of the other curves maybe you can post a file with just the one solid and one curve in it so I can know for sure which particular one is giving you the trouble.

- Michael