Not sure if this is a mansion-specific issue or perhaps something more general.

However, after making it to the first save and quitting the game, i tried to open the save i got a message saying: 
"The mansion file 'Three Way Mansion.zip' could not be found.  Please make sure that this mansion is inside the custom mansion folder, etc."
The same thing happens if the game is suspended and i try to resume from where i left off.

The mansion .zip file is in the custom mansions folder (i even re-downloaded it) and can be opened and played from the beginning. 

Check to see if you're getting to the bottom level folder. There may be a mansion file folder within a top level folder, because that happened to me, too. In other words, there might be a folder inside custom mansions folder with the name of the mansion (folder 1), then another folder inside that one with the same name (folder 2, which contains all the mansion files).

If that's the case, move folder 2 directly to Custom Mansions folder, and get rid of the now empty folder 1. Hope that makes sense.

TWM was uploaded as a zipfile with a readme file and the zipped TWM within.  This means that after you download the file you should have a folder containing the readme and the TWM.zip.  Just drag the TWM.zip to the "Midnight Mansion HD Custom Mansions" folder if you want to play it as a zip file.  If you want to unzip it then drag the unzipped TWM folder to the "Midnight Mansion HD Custom Mansions" folder.

If you system does not automatically unzip downloaded zipped files you must do it yourself by double-clicking it.

So the hierarchy is:

The uploaded zipfile unzips to a folder containing a readme file and a zipped TWM file.

The zipped TWM file can be played "as is" or can be unzipped first to a TWM folder.