I've just installed a new guest book at www.marple-uk.com/av_guestbook/ and I seem to be having the same problem as described in this topic. The link is just to the guest book itself, which will eventually be used within the frame of the main web site.
When I attempt to preview a post and then go back to modify it in IE6 I can't do it. 1 click doesn't do anything (the page seems to refresh) and a 2nd click takes me back to the guestbook. I get the same results if I use the browser back button instead of the one in the body of the page.
When I try this in Firefox it works exactly as I would expect, every time. I can go backwards and forwards as many times as I like between preview and input screen.
Unfortunately I really need it to work with IE as most of my visitors are using it.
When I try this out on your Guest Book on this site using IE 6 it works OK!!
Do I have the very latest script? I only installed it today through the control panel provided by my web host and it appears to be 2.3.1.
I notice that when viewing the source of your preview page compared to mine there is a difference in the naming convention (gb_name / name etc.) - which indicates that perhaps the scripts may be different:
Yours:
<tr bgcolor="#E8E8E8">
<td width="32%"> </td>
<td>
<input type="button" name="back" value="Go Back" class="input" onclick="javascript:history.back()">
<input type="submit" name="gb_action" value="Submit" class="input" onclick="if(flag==1) return false;">
<input type="hidden" name="preview" value="1">
<input type="hidden" name="name" value="Mark">
<input type="hidden" name="email" value="">
<input type="hidden" name="url" value="">
<input type="hidden" name="comment" value="Just a quick message to see how your guest book works.">