I have the same problem as reported by 'hornetster'. Not able to delete the wall. I have just installed it through Sweet Home 3D with Java Web Start. My OS is Ubuntu 14.04 LTS. Version of the Java is given below

java -version
java version "1.7.0_95"
OpenJDK Runtime Environment (IcedTea 2.6.4) (7u95-2.6.4-0ubuntu0.14.04.1)
OpenJDK 64-Bit Server VM (build 24.95-b01, mixed mode)