You have a statament like REPORT.PRINT or REPORT.SAVEAS or something similar somewhere in your code and the report that you are trying to execute has ProcessingOnly property set to Yes.
You have to request your CSP partner to involve their developers to troubleshoot this issue and trigger this error using debugger.
Please be aware that NAV 2013 is out of mainstream support since January 2018.
I would suggest you to be in touch with your Partner / Reseller to orchestrate an upgrade to a supported version.