Refresh failure due to "Error while buffering"

I have 5 models refreshing twice to 6 times a day and all have been working fine for several years. Recently one of them started throwing this error, but only on the refresh run at 3am not the one at 9pm. Another refresh at 4am are fine.  The error message is compeltely unhelpful.  You would think if not enough space on the disk it would become a permanaent error. Any ideas what is causing this and any solution?

Thanks Mike