filter 66 doesn't work for some reason.
(command "ERASE"(ssget "x" '((0 . "INSERT")(66 . 1))) "")
is it a bug?

Hi,
well, it didn't work for unknown reasons.

Try this to filter blocks with attributes:
(command "ERASE" (ssget "x" (list '(-4 . "<AND") '(0 . "INSERT") '(66 . 1) '(-4 . "AND>") )) "")

Did that work? Curious...I will be using that on the regular if it does.