I was doing some testing to compare the SSRS Trial Balance against the standard report version but ran into a problem straight away when I found the SSRS version returned no data.
A quick search online found me this post SSRS: GL Trial Balance Summary report returns no data – Follow Up by Mariano Gomez where he discussed the exact problem I had encountered.
As Mariano says this has been fixed in the upcoming SP3 but for now there is a Knowledge Base article covering a workaround which is to alter the stored procedure (seeglPrintSRSTrialBalance) which is used for returning the data: GL Trial Balance SRS Reports return no data using Microsoft Dynamics GP.