Recently I had a customer who when they tried to open a Word document in their Shared Documents they received multiple prompts from Internet Explorer and Word. This seems to typically happen when the SharePoint site/server is remotely hosted.
What happens is that IE will force this behavior because it does not believe that the SharePoint site is to be trusted. We can work around this designed behavior.
First we have to check to make sure Client Integration is turned on. Go to the following site within SharePoint Central Admin.
Central Administration>Application Management>Authentication Providers>Edit Authentication
Make sure you have the following selected as pictured above.
On the client side take the following actions.
Internet Explorer>Tools>Internet Options…>Security>Local Intranet>Sites>Advanced…
Enter your appropriate domain information>Add>OK
Next navigate to your site and you should receive your normal login prompt.
Type in your account ID, Password, and make sure to check ‘Remember my Password’.
Now IE will believe that the remote SharePoint site is a local Intranet site and pass the credentials as if you were part of the same network.