My wife is having some problems using MyIbay because of the tendency for it to open more than one instance at a time.

I have just checked her system tray, she had 12 different MyIbay instances running, and it seems to confuse your server when she places a bid.

I have unticked the "minimise to system tray" box in Options, I hope that is all that is required?

We are also still getting the error message when MyIbay closes too - something about checking the log file? Is there a fix for this?

We are using WIn 7 ultimate 64bit.

You did not describe the actual problem she got due to multiple instances.
It may confuse a user, but not the server. The latest change takes priority on the server.

The message you see when you close it can be ignore for now, it does not affect sniping. It will be fixed in the next version.

The problem seems to be that the program doesn't snipe in some circumstances. Perhaps it is because my wife is adding her snipes to an older instance which is not updating? I am not sure, but it would be better if only one instance could run. Are there any benefits in having more than one instance at a time?

Will unticking "minimise to system tray" definitely prevent more than one instance happening?

And thanks for letting me know about the error message, it's an inconvenience, not a problem.

Some users have two instances when they snipe under two different eBay user ids. That's the only reason I could think of.

Unticking "minimize to system tray" just prevents minimizing to system tray (when it minimized next to the clock as a little icon instead to the bottom as any other application does).
It will not prevent from running multiple instances, but at least when you see the application is running on the bottom, maybe you will not open a new one.