my HFSS reported LastAdaptive error

Can somebody tell why? Sometimes it disappears but sometimes it comes out. I did not change any parameter of my HFSS project.

Well, then you can increase the number of passes! Go to Solution Setup, under Adaptive Solutions, increase the "Maximum number of Passes".

Well, I already set it as 99 and the maximum delta S is 0.02, still happens.

You do more than 99 passes? Something is wrong with your setup.

Set up a seed mesh so that you only need about 5 passes. Ensure that the mesh refinement per pass is sufficiently high (> 30%).