i tried exporting my map, but it said "Failed to export"
2)Try restarting FH. It worked for me ![Smiley :)](https://feral-heart.com/smf/Smileys/default/smiley.gif)
I'm not much of a map maker but I'll try to offer you the best advice I can. Just as Doctor Flob said closing the FH window and restarting often works but if it doesn't:
It's possible that you're missing an essential file for your map such as the .map file etc. Try double checking to make sure you included all these files and didn't delete any.
You could also have a case where a mesh or particle is not exporting because its file may have been deleted or misplaced. Make sure to check your files to see if you can find which file may be causing this issue and if you can try to restore these missing file(s). You could also delete the object from your object group which as Flob mentioned if it's a custom object must have it's own group.
Also make sure you didn't delete or modify any default files. Meshes etc (basically any of the file which would be the files of the official game download).
Hope something here helps you. Goodluck