FMC "PROGRAM ERROR"

Is there any information on what would cause thise errors in the FMC?Last night I was tweaking my arrival into KPHL via the GVE.DPNT4 arrival (FSB2.2) by adding my arrival runway and on the arr screen, when I added my runway (DILS27L- why 2 identical entries?) and picked the transition, I recieved the dreaded Program Error. At least this time the FMC screen did not totally blank out.I always use FSb for planning and import the plan as opposed to enter it manually (WPT via WPT... ARR) Which I suppose I should do just to rule out the errors :)I have seen thsi error multiple times- specifically choosing either a STAR, transition or approach. (all on the ARR screen)Any Ideas?Tim