"Impossible to open" with ADE

[Silvia24411714ui8w]

Using ADE for the first time to convert an EPUB with DRM. Everything works until I get an error message one minute after the conversion: file impossible to open, there are problems in this element. Already uninstalled and reinstalled, deauthorised and reauthorised. Do you think that the problem is in the file?

[Silvia24411714ui8w]

Please, can anyone help? I thought that the problem was in the file and sent a claim to the supplier, but now it is happening again! I bought 3 e-books in format E-PUB with DRM. One of them was converted successfully, but for the other 2 I got the same mistake message: I convert the files, everything goes well, but after some thirty seconds I get the message "Impossible to open, there are problems in this element". Please note that:

I have already uninstalled and installed ADE one hundred times, cancelled all the files, caches and cookies, reinitialized the computer, de-authorized and re-authorized it;

It is not a problem of the E-reader: I get the message even before connecting it to the computer;

I am using Windows and the latest version of ADE.

Please, please, tell me what is wrong!