The client and server cannot communicate, because they do not possess a common algorithm

Hi,

I added a button 'login with facebook' (app created on https://developers.facebook.com/apps/) in my login page, but I receive this error when i click on this button!

error: The client and server cannot communicate, because they do not possess a common algorithm

please can you help me?

FYI: i used ASP.net 4.0

Did you use a plugin, or did you just embed the facebook button code on your /Views/Customer/Login.cshtml ??
Also, did you set-up and enable External Authentication for Facebook in your admin area?
Configuration >> External Authentication Methods

And maybe you need to first enable the plugin in your site:
Configuration >> Plugins >> Local Plugins >> Facebook authentication >> Configure >> put your app ID/key and secret from the facebook app settings >> save >> enable

Also, it is a good idea to include which version of nopCommerce you are running...sometimes things change from version to version.

I followed these steps:

HTTPS requirement

First of all the server has to be secure - it should have valid SSL Security Certificate for the domain under which it's hosted. This is required by Facebook. (As Facebook says: "Note that SSL support for your page tab app has been mandatory since October 1, 2011.")

Facebook Developer Application

The first step is creating an application in Facebook. You can do this by going to https://developers.facebook.com/apps/. Click on the "Add a New App" button.
Go to the advanced setup. Choose a Name for your app. Next, choose a category. You should select "Apps For Pages". Click on the confirm button. Now you will be redirected to your app page.
Go to "Settings" from the left navigation. Click on the "Add Platform" button. Select "Page Tab" platform option. Now you will see a section called "Page Tab".
Enter the site of your shop in the Site URL field like this: "http://www.yourstore.com/facebook/store/". NOTE that the url should be with HTTPS and the suffix "/facebook/store".
By default the "Page Admin Control" and the "Wide Page Tab" are enabled. Leave them this way and save the changes.
From the left navigation > App Details, you can add images and icons for your app.
Including your app on your Fan Page

Navigate to the following URL in your browser: https://www.facebook.com/dialog/pagetab?app_id=YOUR_APP_ID&redirect_uri=YOUR_URL
Replace "YOUR_APP_ID" with your App ID and "YOUR_URL" with your app's URL, both of which values are available in your app settings.
You'll see an "Add page tab" page. After selecting your Facebook page from the dropdown menu and clicking "Add Page Tab" your iFrame app should appear on your Fan Page. You can manage it from the Manage Tabs.

Yes, that is the first step....to create the App at Facebook.
The next step is to configure your nopCommerce application, as I described.

You must have "credentials" set up at Facebook, but you must also have your nopCommerce "login system" working in tandem. When you install the facebook authentication plugin and properly enable external authentication in your nopCommerce settings, it allows your site to retrieve details from Facebook to authenticate the user as a registered customer.

Configuration >> Plugins >> Local Plugins >> Facebook authentication >>

and

Configuration >> External Authentication Methods  (enable facebook authentication)

all these steps done, but i still receive the same error, maybe it's related with the SSL code and needed to add some codes?

Maybe...
the information you pasted above DOES say this:
Enter the site of your shop in the Site URL field like this: "http://www.yourstore.com/facebook/store/".
NOTE that the url should be with HTTPS and the suffix "/facebook/store".