Your error is an FAQ; if you only run poly selection in stages then unless you run the stage 2 root sieve you will not assemble a complete polynomial. By default the NFS driver in Msieve assumes you want to do the whole factorization, so not having a complete polynomial is treated as an error. It actually is silly to do that, since even if you did have a complete polynomial the sieve code in Msieve is probably an order of magnitude slower than the highperformance lattice sieve that a script calls an external binary to perform.
In the past we have had students complete big factorizations (i.e. 160 digits) in a remarkably short time, by taking over idle computer labs. On modern machines a 170digit factorization starts to get into the range where the linear algebra is a major headache to perform in a reasonable time, i.e. it will take weeks unless you use MPI and have a few machines with a highspeed interconnect (gigabit ethernet isn't enough).
