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:
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Code source
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1
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Папка для пользовательских аддонов
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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.