I am very new to SSRS and am trying to generate a report using SSRS, I am able to pull the data on to the screen without any issues but when I try to export the data to an excel file, I am getting an error "The row item structure object corresponding to a line cannot be null" when there is data that spans multiple tabs in an excel. I am able to export to any other formats eg: PDF. After some googling I found that there is an issue with the SQL Server reporting version and Microsoft mentioned that they will release a patch to fix this issue but I dont see that there was any patch. I am using SQL Server Reporting Services Version 2007.0100.2531.00. Any pointers will be of great help.
Depending on the version of SSRS you're using, it might be the problem described in this post on Microsoft Connect, which should be fixed in later versions of SSRS.
Also, it can be something with page breaks, or, as in my case, matrixes without data. When I hid the matrix without data (with =CountRows("MyDataSet") = 0), the problem was solved.