I have tried your fix with the attachment provided by you. Unfortunatly Log file "Aspose.ReportServices.log" is not created in "LogFiles" folder of ReportServer and I got the same error (i.e. An unexpected error occurred in Report Processing. (rsInternalError) An error occurred during rendering of the report. Object reference not set to an instance of an object.)
Than after I have manually created the file "Aspose.ReportServices.log" in "LogFiles" folder of ReportServer and tried to get error details in this file but I was not able to do so.
Thanks for your help & support. I am glad to inform you that the fix (of version 1.0.0.3) provided by you is working and now I can able to download data from report to excel using Aspose.Cell (for all 3 options provided by Aspose.Cell installation).
However, one problem reagrding format is occured. In my report, one of the field called "Cost" has value like 56.00. this value in file generated using Aspose.Cell is diaplyed as "g".
On analyzing further it has been found that, the format of this cell in excel file (generated by Aspose.Cell) is considered as "Custom" instead of "Number". For same report, file generated using "Excel" displays correct value. Also in log file for Aspose.cell in LogFiles folder of MSSQL reportingservices contains correct value.
Herewith I have attached all three file for your reference in one Zip file as "CategoryReport.zip". Which are as follows:-