Searching for this issue you will find the following technet solution:
http://technet.microsoft.com/en-us/library/gg731894.aspx
The SSRS Service Account password could be invalid.
- From the Start menu, point to All Programs, click the SQL Server folder, click the Configuration Tools folder, and then click Reporting Services Configuration Manager.
- In Reporting Services Configuration Manager click Connect and then click Service Account.
- Set the password and then click Apply. The account and password should be the same as the Microsoft Dynamics AX proxy account. For more information, see Before you install the Reporting Services extensions.
- Click the ServerName/MSSQLSERVER and then click Stop. Then click Start to restart the server. Always check with the SQL administrator and make sure no other users are connected to the server before you restart the server.
<service>
....
<isrdceenabled>True</isrdceenabled>
</service>
So keep in mind to also check the configuration of the SSRS installation. A missconfiguration could also lead to these label issues.