In SimDash version 1.3.1, the format of RevBurner configuration files changed slightly, resulting in the error message "The loaded configuration file is not valid" when importing a file created in an older version of SimDash.
The solution is to open the configuration file in a text editor (notepad will do), and editing both the second and last line, beginning with "<Settings xmlns" and "</Settings>", to "<TachometerSettings xmlns" and "</TachometerSettings>" respectively.
This is necessary for both RevBurner and RevBurner for Speedometers configuration files when importing from an older version of SimDash.
I had this problem after installing 1.3.1 and figured I'd post the solution in case anyone else ran into it.