Star/Runway change in flight not working

As with 99% of the NGX users out here, I'm ecstatic over the performance and quality of the NGX. But, I found a little error on my system when I decided to change the runway/STAR shortly before the T/D and wanted to know if this is a common occurrence, or if it's isolated to just the Navigraph data for the airport. I normally never change the arrival runways once I'm in-flight, as 90% of the time the weather is constant and would not necessitate a change. But I noticed a windshift on the ground, and thought I'd give it a try. Route was KSLC to KSEA, and as with all my flights, I loaded the landing runway (ILS34C) and STAR (CHINS7) before engine start. ASA weather depicted northerly winds (the 34's) at takeoff, but sometime in cruise it reversed direction, and even though it was only 3 knots, I wanted to align myself with AI traffic which was going to use the southerly 16's at KSEA. About 100nm from T/D, I go to arrival/dep page in the FMC to change runway from ILS34C to ILS16C, but I received a message along the lines of "ARR N/A FOR RUNWAY". IIRC, in other Boeing FMC's I should be able to change to any runway from the list, and then pick a corresponding STAR and transition as I wish. But for some reason, I could not go past the FMC advisory message. I tried all kinds of tricks, but ultimately things got so messed up that I lost all altitude/speed predictions on the legs page. I decided to cut my losses and just restart the flight where I left off, thanks to FSUIPC autosave, and finished my flight with the originally programmed runway and STAR. Any ideas? Are runway changes not permitted close to T/D? Is this a bug? I will note that I never suffered a CTD, which I was afraid might happen. I voluntarily exited and restarted.I may try this situation again tomorrow to see if it was an isolated incident.