The message is pretty explanatory. Your report has a paramter ‘path1′ which cannot be null, and in this case it is.
If you are calling your report from another application, review the code of that application to see why it is sending a null value for that parameter. To debug it, you could display a message box or alert to show the value that is going to be sent for that parameter before calling the report.
If you have already done that, or there are other troubleshooting actions you have already performed, please provide more details.