If you receive the following error when running an SSRS report –

“An exception of type MetdataException has occurred while performing the operation.”

– the issue most likely has to do with the AX datasource metadata.  One such possible cause is an incomplete definition of a relationship on a table.  For example, we ran into this issue when printing the Project Invoice Journals report.  The report was not customized, but it turned out that the datasource table was customized by a previous implementation partner.  A table relation was added to the ProjInvoiceJour table, which contained no lines.  Fixing this relationship resolves the metadata issue.