There were people having the same problem when 4.0 hit, but I forgot the solution. Try the following things:
First, make sure it's the right Allods folder. With the new patch, you might have installed Allods in a different folder.
After that, make sure the folders are named right. It's case sensitive. The folders are data/Mods/Addons.
If that's ok, make sure you have a readme.txt file inside the Addons folder. If you do, open it and make sure it contains this:
	
		
			
				|   | Code source | 
			
				| 1
 | Папка для пользовательских аддонов | 
		
	 
 
If the file doesn't exist, create it and copy->paste the above line in the file.
Too bad the old NA forum is not accesible anymore, there was a good troubleshoot guide there.