I seem to keep having this problem.

Typically I have reasonably complex moulded plastic part, and I have an overmoulded EPDM part which needs to conform to the other part. Typically I use these for seals and waterproof button actuators. parts are designed in a top down assembly using sketches on  planes at the top level for layout.

When the assembly is designed and I go back to make some minor change, the most recent was to change the rotated profile of the button actuator slightly, now when I roll the feature tree forward, the indent (cut) feature which had previously worked "can't handle this case"

I've attache a screen grab of this case. The boss with the threaded insert is supposed ( and used to ) cut out the donut looking thing above and to it's right.

Does any one have any suggestions how to fix this or what might be causing the fail, or alternate methods?

I thought of a combine subtract, but it is greyed out.

Thanks for any input

Graeme