[greigeh]

This would require looking at the full coding of the skin, it seems there might be an issue with the style storing the Cookies or something like jQuery isnt operating properly.

Alternatively, if you have a rough idea about vBulletin coding - you could set up a userfield in which has options of "Hide" & "Display Sidebar", simply using coding such as:

<if condition="$bbuserinfo[fieldID] == 'Hide'">
<style>
.sidebar-CSS {
display:none;
}
</style>
<if>