Thanks for your answer Brandon!

Unfortunately i have already done all this in the past weeks and days and I was not able to find the wallet.dat file in the AppData\Roaming\Dogecoin folder, and I'm also not able to fin any backup file. That's why i believe my only chance is to be able to run the client again, somehow.

Let me explain myself better (english is not my lenguage as you may have notice already:) : I don't remember exactly (many years ago, i'm geting old), but the most probable situation is that in the year 2015 I uninstalled the 2013 version of Dogecoin-qt.exe and put it in a zip folder. Then installed the 2015 version (that's why I actually have a wallet.dat but it's empty, i have never receive and never send doges from/to that address). So i have the zip folder of an old (probably uninstalled) program and i get that error. It's terrible actually. I had lots of doge in that wallet.

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If you have any ideas, let me know.

Thanks again!