Do you have the latest version installed?
How much memory do you have in your computer?
According to the webshots site:
Webshots Desktop 2.0 in Full Screen (foreground) - virtually 0% CPU Usage, 12 MB Memory
That's the requirement...
Also try disabling and then re-enabling the cycle of the pictures:
# How do I make my wallpaper change automatically?
To enable wallpaper cycling:
1. Open the Webshots software by double clicking the Webshots Desktop icon on your desktop.
2. Click the Options button.
3. Under the Wallpaper tab use the drop down menu next to Automatically Cycle Wallpaper Every for selection of a time.
Webshots must be in your tray for your wallpaper to automatically cycle. To enable your tray, open your Webshots software by double clicking the icon on your desktop.
1. Click the Options button.
2. On the General tab, check the box next to "Show tray icon".
3. Click OK to save your changes.
Another thing, is try to create fewer pictures to cycle through... that might fix it... even though you may want to look at 75 pictures on a rotation, it might be that you have to settle with half that amount to keep the webshots software functional.
If you have a premium membership with webshots you can contact them directly: