"Object reference not set to an instance of an object" error!!!

The error "Object reference not set to an instance of an object" will give reporting developers fits as it is cryptic with no real indication of where the issue is.  This error has been rearing its ugly head to me in the last few dayswith an SSRS report using a Dundas chart. The error occurs at runtime so all of the parameters are entered successfully but this error is coming from the Dundas chart. After much consternation I did figure out what was causing the issue. It was simply the fact that the parameter I was entering in the report was set up as a multi-value parameter but I was using the parameter in the Dundas chart as a single-value parameter. I was using this parameter in an expression field for the X minimum value for the X axis.

After I modified the report parameter and made it a single-value the error was gone. I certainly learned a valuable lesson. More often than not if you receive this error with a Dundas chart the first thing to do is to check your parameters and ensure they are consistent when they are set in the report and where they are utilized in the Dundas chart setup. Just search on the above error on this site to see a more detailed description of this error and resolving it...