Just curious, how are you exporting in a JPG format with NPrinting? I see all kinds of export formats using a task, but JPG is not one of them.
Does the problem happen with just charts or does it happen with straight tables too?
I have had export issues with images when the user preferences were not set to output. In the Copying to Clipboard section, you need to have the object type selected that you want to export. These are not selected by default and they also need to be setup for each user. So, if you are using a Nprinting service account, you would need to login to your QV desktop client on your Nprinting Server with the service account and set these settings.
Give that a try and see if it helps
Any reason why you are choosing Qlikview Entity Reports to send these?
It seems unusual to use Nprinting to distribute a report you created in QV.
Are you posting to a web site and need JPG files? You can use any of the other templates and generate a PDF that has your images from your charts and it would be pretty easy to setup. Word or PPT would be the logical formats.