since the exporter is not updated for a while, i suppose that the issue was related with the internet licence and old octane versions.
as Proff54 pointed out, detaching from the net was a workaround. newer octane versions doesn't have this issue, infact it's a couple of months that i'm rendering 200 frames and more on 4 different pc's every night without any problems with R13 and the old v11c exporter
ciao beppe