Simulation using pspice requires a pspice mathematical model of the component which tells the software how the comp reacts to the input. These models are present in the pspice library only, the other components in other libraries dont have these models. They are for design only, not simulation. But u can normally find all the components in pspice library, LM317 is present in the national semiconductor library in pspice.
To find whether a component has a pspice simulation model or not, always check the lower right corner of the 'place part' window, below the component image u will find icons, bringing the mouse pointer to which will reveal what that icon is for. Simulatable components have a pspice icon with them. Similarly those components that have footprints assigned to them have a layout icon with them.