This is probably due to an issue with the SST2 output format (since resolved - I think it was fixed in a later subversion). I'd suggest you use:
envSetVal("spectre.envOpts" "simOutputFormat" 'string "psfbin")
If you do this, I'd suggest you do a Simulation->Netlist->Recreate before running a simulation.
Thank you, Andrew.
It is working. I also found that if I closed the icfb (or msfb) window and started Cadence from scratch, it also solved the problem (until it rears its ugly head again!)
If I remember rightly, the problem is caused by running a short simulation and then a longer one - something in memory is not correctly updated and hence it does not realise that the stop time is longer. So quitting and restarting would fix that too. This only happens with SST2, and only if the change in stop time is significant enough.