If you have custom workflow or application which renders SSRS report in CRM and generates PDF or excel as output and it you are using the same user to connect reporting service and generate this report then if you bulk generate lots of records then CRM throws following error on report server.
The report server has detected a possible denial of service attack. The report server is dropping requests for service from the IP address XXX.XX.XXX.XX.
This is because reporting service by default allows only 20 requests for same user. This is setting in Reporting Service configuration and you can update to your required value to fix this issue. (see below screen print for the same which updates value to 250)
Above reporting service configuration file can be found in C:\Program Files\Microsoft SQL Server\MSRS10_50.MSSQLSERVER\Reporting Services\ReportServer folder.
For more information on all Reporting service configurations please refer following article
Hope this helps..