Looks like the problem may be with the amount of available RAM on the server, apparently at some peak times there are huge numbers of people accessing at the same time, which is causing the failures.
We have written to Clive Sinclair to see if he can provide an upgrade to the ZX Spectrum we are using, and await his reply.
More seriously though, I believe an upgrade should be carried out in the next couple of days which should ensure continued availability.
Rolf