Are you using Windows? Is it the trial version?
Viewing post in The Transforming Detective comments
According to a Reddit forum, the RPG Maker game may not be able to save if the game folder is located in a restricted directory or if the save folder is set to read-only. Please try following:
・Move the game to a writable location such as the Desktop or Documents folder.
・Right-click the game executable and select “Run as administrator.”
・Check the properties of the save folder and make sure it’s not set to read-only.