Default Application Pool - Access to printers

Hi Everyone,

I have a network printer in which applications on my Windows 2008 Server print to. I've found that my applications will stop being able to access the printer causing applications to hang or crash. To fix this problem I only need to go into the Default Application Pools settings and change the Identity from Network Service to another Identity and then back to Network Service to be able to print to the printer again. Does anyone know what might be causing the application pool to lose the right/privledges to print to a printer like that? 

Thanks