I'm not familiar with the tool you're using. The location it's attempting to access for the icon storage is the normally-correct place on XP (assuming Opera is installed for use in the 'owner' user account). Have you checked in Task Manager to make sure Opera is really not still running a process that has locked its files, even though Opera appears to be off? Also, are you sure Stu's Tool has permissions-access to the named folder(s)?
In any case, there should be no reason you couldn't manually copy the entire contents of the folder to the new Opera installation (assuming its version is the same) after exporting all the other Opera settings via the tool. It's also possible that the tool itself is simply unable to handle the task for an Opera installation, for some reason. In which case, this error may be just the first of a sequential series of similar blocked file access error messages from the tool. In that case, you might be better off simply copying all your personal Opera data files manually to a new installation on the new drive.
With Presto Opera, personal data files can readily be manually copied from one system to another. I've personally done it numerous times.