While access dashboard from portal. the following error occours.

An error ocurred while accessing application id tfs from Secure Store Service. The following contents failed to refresh: TfsOlapReport

To figure it out ,you need to

Enable Claims to Windows Token Service

1. In Central Administration, in System Settings, click Manage services on server.

2. Select Claims to Windows Token Service, and then click Start.

3. Verify the service is also running in the Services console:

   1. In Administrative Tools, click Services.

   2. Start the Claims to Windows Token Service if it is not running.

2. Configuring Secure Store Service (SSS)