Genexus error "Check srcIndex and length, and the array's lower bounds" generating report

KB built on Genexus 16 U9, using generator .NET 4.0.

The system generates a report when the client request via web service, passing the invoicy's ID. Generaly it's requested simultaneously for many different docs, but every report generates an unique filename (avoiding lock the filename), converts it to base64 and delete the file.

In majority the request goes success, but sometimes it starts throwing the exception below for many requests in a short period of time. After recicling the IIS pool, it stops occuring for a while.

Report procedure: rnuc006.

Source array was not long enough. Check srcIndex and length, and the array's lower bounds.   at GeneXus.Procedure.GxReportUtils.GetPrinter(Int32 outputType, String path, Stream reportOutputStream)
   at GeneXus.Procedure.GXProcedure.getPrinter()
   at GeneXus.Programs.rnuc006.executePrivate()
   at GeneXus.Programs.rnuc006.execute(SdtSDTDadosEmissao& aP0_SDTDadosEmissao, SdtSDTDadosEnvio& aP1_SDTDadosEnvio, Int16 aP2_indiceLote, Int16 aP3_indiceRPS, String aP4_Filename)
   at GeneXus.Programs.pnfs216.S121()
   at GeneXus.Programs.pnfs216.executePrivate()

I'm trying to debug, but its dificult to find why it starts happening suddenly.

Solution

There's a fix to this error on v16u10, maybe you can try with that version if you have this problem again.