'Cannot find material hay'
I think there are a object in a object group who is basewhite and missing a material, maybe you are not using that object in your map, but if it exists in the object group can pop-up to you that error.
Alot of the objects I had on the map disappear when I am on FH checking it out and not on Map Maker itself.
That problem can happens when you modify any of the objects groups that comes by default in the game, i mean these objects groups:
Default.object,
MyPlants.object,
MyRocks.object,
MyTrees.object.
And when you have some exported maps from other people, the "extra" objects you added in these objects groups can disapear.
The solution is to move any custom object to a new object group of your own.
If you spent a lot of time doing your map and you need help with moving objects to a new object group, i can help if you send me the files by PM or email (every object group and your map files).