If you downloaded Galaxy Forge yesterday, I presume you have the most recent version.  Double-check that your game is also updated to the most recent version (1.16), since the map file format has changed in more recent versions.

My map directory is here:

Put all your galaxy maps in here and they should run fine if you have the most recent version of Sins.

1) do you have the most recent version of sins?  (1.16)

2) do you have the most recent version of galaxy forge? (version 3; you can check by opening a .galaxy file in notepad, it will tell you the version number in the second line)

If you're running the latest version of Sins, then maps created by the latest version of GalaxyForge should be working.  If not, the most likely cause is that you are running either an old version of GalaxyForge or an old version of Sins, and the map version being produced is incompatable with your game version.