ERROR: Unable to write file : DISK_ERR, leads to Out of Memory errors.

Is there any way you can check what the sector size on your SD card is? It should be 512...

Thanks for all the info - it'd seem that the issue is still that something strange is happening with the value from getTime() judging by the values for time in the timers array. It could be that rapid changes of the time are causing the filesystem library to time out before things are being written correctly.

I've spent ages trying to sort that out for 1v57 though - I've had a board running over the weekend as a clock, and it's still keeping time - which seems a definite improvement over 1v56.

Can you try:

var t = getTime();
if  (!fs.appendFile("timetemp6.log","DHT11,"+t.toString()+","+rh.toString()+",Time,"+getTime().toFixed()+"\n"))
 console.log("FAIL before "+t+" after "+getTime());

That might help to show whether the time is actually being reported wrong...