I solved this issue by temporarily bypassing my proxy.

I Finally got mine to work. I hadn't changed anything on my computer,  but it just started giving me this error and the E_ADEPT_DATABASE error  out of the blue. Nothing really worked. I tried redownloading the  program, restarting my computer, changing my internet settings to  "automatically detect...", yelling, anger, sadness, evil eye.. you get  the point. Anywho, after several successful attempts, this is what works  for me:

By the way, I run Win 7 and mainly use ff. Unfortunately, FF does not work with this.

1. Using the search bar in Win 7, type in "Allow". This should pop up  the link to "Allow a program through Windows Firewall". Clickety-click.
   
2. Click on the button that says "Change settings". (Maybe be fast or slow).
   
3. If Adobe Digital Editions is listed, click it (I have  home/work checked but not public). If it is not listed - Click on "Allow  another program.." (really that what the button says. Find Adobe  Digital Editions and click.
4. Click on OK.
5. Open the acsm link through Internet Explorer (FF won't work). It should download no problems.

I have tried this with FF and it did not work. I had to go back and "Allow" ade again.

Works in IE if I automatically detect... or not.

Is still annoying because it worked fine before. I want things back the way they used to be!

I know that this is somewhere on the Adobe site but I had a hard time finding it.

I know I talk too much but wanted to explain in detail (yes, I know it's a lot of detail.

I have a mac, running firefox and I cannot change my proxy settings as then I will have no internet at all. Can anyone tell me how to fix this?

I had this error occur.  I was on Google Chrome when I downloaded ADE.

Found this forum, recognized that the browser could have been the problem.

I uninstalled ADE, opened Microsoft Internet Explorer,

downloaded from there, and ADE installed and opened without a problem.

Thanks for your help, forum people!

plz... help me...

i having the same trouble, i cant activate my ADE and keep getting this error message

i've done almost everything that has to be done but i just couldnt activate it

plz help me
by the im using Window Vista

I just ran into this problem on my old Vista laptop. When I first installed ADE 3 weeks ago, it worked fine. As of yesterday, I started getting the E_ADEPT_IO error whenever I tried to download an ePub book via .acsm (the ADE link format). Since first installing, I'd updated Firefox and I might have installed Vista Service Pack 1 (possibly before installing ADE though).

I didn't even think of trying a different browser, since it doesn't really make sense that the browser would affect the .acsm file -- I tried downloading the .acsm to my hard drive and opened it from there, and got the same error. I turned off that stupid User Access Control and added ADE to the firewall exceptions, but no dice.

I had to fire up IE for something else, and tried again by opening the .acsm link directly in the browser. It worked fine. Go figure. . .

This was helpful. I run Windows 7 and had the same problem. I uninstalled and reinstalled the program and turned off my firewall but ran into the same problem until I right clicked on ADE in the start menu and clicked troubleshoot compatibility. The wizard switched the settings to the Windows XP Service Pack 2 settings and it worked brilliantly.