As many backup programs today, NW uses the UNIX time in the background (counting in seconds from 01/01/1970).
My personal guess: you defined a date beyond the 32bit barrier which will appear around 2037. Obviously all programs will at least use 64 bit by that time.
IMHO - Setting browse & retention date 100 years ahead is nonsense. Nobody knows whether still soft- and hardware will exist to support that. You have to copy it in the meantime anyway to convert the data and at least refresh the information. And of course it increase the needed space for the index directory. But EMC would love to sell you more disks, of course.
However, if you really need to keep the data that long - eject the media, set the write protect notch and store it in an air-conditioned room offsite.