What kind of service account are you using? Can you connect to the OLAP instance using SSMS? If it's not on a local machine, did you check your firewall settings to see if the port is available? From the article:
In SQL Server 2012, depending on the operating system you are using, the service account might be NetworkService or a built-in virtual account created for a specific Analysis Services instance. If you choose the service account for a connection that uses Windows authentication, remember to create a database login for this account and grant read permissions, as it will be used to retrieve data during processing. For more information about the service account, see Configure Windows Service Accounts and Permissions.