NVi and Remote not speaking to each other...

I've had the problem many times of the remote not working, usually fixed by doing a reset as advised in the FAQs.  This time I've done a remote reset, and then reset both the remote and NVi but with no effect.  The message on the NVi screen says that the AV system code has been reset but although most of the remote buttons seem to work, the up/down and left/right arrows do not work.  They have the effect of  changing the input (disc, digital, analogue etc) or mode (auto, mono, stereo etc).  Not a lot of use when you are trying to work your way through DVD menus!  I've even tried powering off the NVi and changing the batteries on the remote.

Anything else I could try?  All suggestions very welcome

Thanks

Robin