When trying to preview any report, the following error occurs:

FrameworkException
The request failed with HTTP status 401: Unauthorized.

Module:System.Web.Services.Protocols.SoapHttpClientProtocol
Method:ReadResponse

Cause:  

If the problem affects all users and all reports, it could be caused by incorrect specification in Weblink.

Resolution:

1. Log onto the Web/Application server as administrator.
2. Launch Weblink
3. Log in.
4. Select the correct Vision database.
5. Click the Report Server tab
6. Click Test > Report Server Configuration.
7. Correct the information specified, if it is not successful

• The account must be a valid Windows user.
• It does not have to be a Domain account if all processes are run on a single server.
• If access to multiple servers is required, the account should be a Domain account.
• The account should have a strong complex password that will not change. 
• This account should be the same as the account which is running the DeltekVisionAppPool.
• This account must be a member of the local Administrators Group on each server
• This account must be a member of the IIS_IUSRS Group on the Web server
• This account must have the Local Security Policy > User Rights Assignments:
  • Log on as a Batch Job
  • Log on as a Service
• This account must have the Security Role of Sysadmin on the SQL server (or explicit dbo rights to each database)

1. Using a SQL account that has the Security Role of Sysadmin (or explicit dbo rights to each database) since SQL authentication is generally faster than using Windows authentication for communication between servers.
2. Make sure that the name of the Report Server database matches the one that is actually being used for the Reporting Service.
3. Click Test > Report Server configuration from the menu
4. Click Save, once the test is successful