I think you will find that using gmp_ecm requires make a special build the the factoring program itself, ecm.exe, on windows machines. The standard build allocates space on the stack for efficiency, and SOB size numbers cause stack overflow. There are compiler options to avoid this, and there is a promise that a future release of ecm will do smarter allocations to avoid this problem.Originally posted by Mystwalker
With these, it is possible to do automated P-1 factoring using either gmp_ecm or sbfactor.
However, the newest version of ecmserver/ecmclient also supports sbfactor instead of ecm as the work engine. That should work.