RTP shouldn't have anything to do with this, much less the one for VX Ace.
Disclaimer: I can't guarantee anything I say will work as the download links on this thread seems to have been replaced by someone from F95, and I can't 100% know everything is as it should be. It probably is fine, but I'll say it nonetheless. Also, none of the following is meant to be condescending, I just have to go step-by-step because people often miss these things.
- With that out of the way, make absolutely sure that you extract it from the .zip file. When you then go to play the game, you go to the folder you extract from the .zip file. People have made the mistake of extracting the game from the .zip but then still launching the game from the .zip - where it can't save as a result.
- Make sure you're extracting it to a spot you know you have all the proper permissions. A safe bet would usually be the desktop.