After applying hotfix KB3194725 to our SQL server, the SSRS server throws the following exception when trying to generate a report:
Exception type: InvalidReportServerDatabaseException
Exception message: The version of the report server database is either in a format that is not valid, or it cannot be read. The found version is '164'. The expected version is '163'.
Based on the version that you got which is 163, try to apply this query on the
instance hosting your reporter server database.
In my below example, the database is named ReportServer :
USE [ReportServer]
DELETE FROM ServerUpgradeHistory WHERE ServerVersion > 163
This can be fixed by applying the same hotfix to the SSRS-server.