I ran into a related issue when troubleshooting a Drupal 6 site that had been recently upgraded to a newer version of views and views slideshow. In the process, the existing slideshows had stopped working.
The problem was that Views Slideshow 2.x for Drupal 6 was changed from the earlier versions and the new version (6.x-2.4) requires you to also enable one of two sub-cmodules: Views Slideshow: SingleFrame or Views Slideshow: ThumbnailHover in order for it to work. Here's the relevant section of the Views Slideshow 6.x-2.4 readme file:
The Views Slideshow module is a Views Style Plugin that can be used to output
Views in a jQuery slideshow.
There are currently 2 modes:
In SingleFrame mode slideshows are output as single elements and controls can be
displayed as numbered links or thumbnails of individual fields.
In ThumbnailHover mode slideshows are output as node teasers or full nodes. The
controls for advancing the slideshow are nodes too.
Further details about each can be found within their respective directories.
I enabled SingleFrame and set it up in the view and the slideshow worked again.