Viv,

it looks like I've found the problem using your suggestion:

>For testing, try firing the method from a button after the WPF load is completed - maybe the report viewer is trying to show something before WPF is ready (but as before I know nothing of the Report Viewer behaviour).

I am now getting a better error message stating that it could not connect to the database server. Which makes sense as I created the dataset against my database which is named differently, of course I had thought that it would pick up my connection string from my config, which was pretty stupid of me. So now I need to research how to get the dataset to use my connection runtime string.

Update

Got It! Apparently the dataset creation added a new connection string setting in my app.config file, once I added that in to the production config file it's running!

Yay, now on to the next problem...

Thanks to Viv and Paul for helping push me in the right direction