Error "Not Enough Space" When adding predefined load to moving load?

Good day, 

I am trying to model the wheel loads on the transverse section of a bridge. I have successfully created the moving wheel loads but I also want to apply the beam dead loads also. 

I attempted to do this by first creating the dead load case details and then editing the moving load generation by adding the dead load case to the "predefined loads to be added" drop down menu. 

When I add the dead load case to the predefined loads I get an error stating that there is not enough space. 

Any help will be appreciated. 

Please find the Staad pro file attached. 

(Please visit the site to view this file)