Run report "attempted to issue a client callback"

I am using a console application which runs specified reports/codeunits from Dynamics NAV 2013 version. The process is done by passing parameters down fromt he console application to the published web service. I can run some objects, but this one is causing me a bit of trouble to get going.

-OnPreReport-
rImportExportEngine.GET('Export');

tFileName := rImportExportEngine.GetFileName();

tSeparator := FORMAT('|');

// create file
CLEAR(fOut);
fOut.TEXTMODE := TRUE;
fOut.CREATE(rImportExportEngine."Folder Path" + tFileName);

-OnPostReport-

fOut.CLOSE;
COPY(rImportExportEngine."Folder Path" + tFileName,rImportExportEngine."Archive Folder Path" + tFileName);

The code did contain an excel buffer, but I removed it. Any clue would be great.