So, several weeks after moving to a new server it emerges that there is an issue with logging on a certain small group of Chrome browser / operation system combinations. ( Not all versions of chrome / and just windows 8 ) . I am aware that this is probably an issue with Chrome and the way that it handles cookies.

Usually, I'd immediately try changing:

Add period prefix to cookie domain

Which is set to true at the moment.

My question really is that on a live store how is that going to effect existing customers? How is that going to effect customers who are actually on-line at the point of change?

It is a busy store but obviously I can make the change in the early hours of the day and avoid having too many people online. Is that the best way of proceeding?

Dr Byte, maybe?