Typically an issue inside of your RDL. Your best options are to enable Remote Errors or go to the SSRS Server and look in the logs.
The SSRS log file can be found in C:\Program Files\ Microsoft SQL Server\MSRS12. SQL2014\Reporting Services\LogFiles (for SQL Server 2014)
They will have all the details. Also if you pushed Sync Dataset that is probably your problem. (Try the Base SSRS Style)