if you failed to download RTP, you cannot access the debug room either. Please try once.
Make sure you have your RTP in C:\Program Files (x86)\ASCII\RPG2000\RTP or C:\Program Files\ASCII\RPG2000\RTP in your computer.
There should be オブジェクト1.png in "Charset" folder too.
If there is not, please try re-downloading it into that directory.