I'm posting this in case someone has the same problem I've just had.
Leadbolt have changed their Ad integration and when you add a new app, they now show by default their Network Direct Deals Ad code. This is in the form of an API key, which Fusion users cannot add with the current Leadbolt object.
You now have to click the 'Add Section' green button. Then choose the 'SDK Ads' tab and click on the 'App Ad SDK' which currently is the left picture of two.
Then for my games I choose the 'Interstitial' tab, click on the single 'Interstitial' graphic and then the 'Add Now' button at the bottom.
Then your game in the dashboard will show a 'Get Code' graphic under the 'Actions' heading. Mouse over to show 'Get Code'. Click to get the 'Section ID' number which I copy and paste into the 'Standard ID' box of the Leadbolt Object properties.
Bit of a performance but I use Leadbolt for my interstitials, as whatever I do, the Admob Interstitials, still always freeze my apps. Admob banners work well though. The old Admob object dating back to early last year showed Interstitials well but every update since then, they freeze in my Apps.
Just for the record, I notice that others have had good results with Chartboost, so I tried them recently and was very unimpressed after several thousand Ad impressions. Leadbolt aren't brilliant but they earn me much more.