From what I can tell in the picture... it looks like you're not using the tabs control properly.
Click the Tab Control Tool button to create a new tab control and drag an area where you want the information to be displayed - this should be entirely within the body of your layout.
Then just drag or create new fields into the required tab.
I just tried and you can have the tab object over the header and body.
With versions older than FileMaker 13, tab controls that extend into the header do not display correctly. If in v13, they do not display correctly when web published, so I still advise keeping the tab control fully within the body of the layout. With a layout like this, you may want to remove the header all together.
To add a new tab panel to an existing tab control, double click a blank area of the tab control while in layout mode or select it and choose Tab Control Setup from the Format menu.
To add fields to a tab control, drag and drop from the field tool or drag and drop from FileMaker 13's new Field Picker.