Hi,
That means that the R server session has died, most likely because of (server) memory shortage. That is a common issue when computing with all data in the R memory. Either increase the memory of the (hardware) server. Or find a way to make your computations in a memory efficient way (depends on your data structure, data source, and type of computations). You can also remove the unsused R objects from your server-side R sessions with ds.rm(), to release some memory.
Regards
Yannick