lopnet = hou.node("/stage")
matlib = lopnet.createNode("materiallibrary","matlib")
mask = voptoolutils.KARMAMTLX_TAB_MASK

matname = "test"
mat = voptoolutils._setupMtlXBuilderSubnet(destination_node=matlib, name=matname, mask=mask, folder_label='Karma Material Builder')

hou.OperationFailed: The attempted operation failed.
Cannot delete nodes while cooking