This is a bug (
Close the program and delete these files:
c:\Users\[Username]\AppData\Roaming\ZennoLab\ZennoPoster\4\ProjectMaker\ProjectEditor\EditorLayout.xml
c:\Users\[Username]\AppData\Roaming\ZennoLab\ZennoPoster\4\ProjectMaker\ProjectEditor\ToolBoxLayout.xml
After, start PM again