E_LIC_LICENSE_SIGN_ERROR

I've bought an ebook from an italian site (libreriauniversitaria.it) and iv'e downloaded it. The file extension is .acsm, and the site says that's "my personal key to download the ebook". The ebook is protected with DRM (Digital Right Management). The site also says I have to open the ebook with digital editions and it will be ok.

So I've installed Digital Editions and I gave the authorization to open the file without signing with my adobe ID. But when I open the file it gives me this (see the picture): it says "impossible to download. Error in recovering the license. Communication problem with the license server. E_LIC_LICENSE_SIGN_ERROR."

I've tried to unistall the program and to install it again (like 5 times!!) but now the program doesn't open anymore the window in which I can insert my adobe ID.

PLEASE HELP ME resolve this!!

Many thanks

dI