Error message when adding item to basket

We have been experiencing a display problem on our website for several weeks now. Some out of stock items are being displayed as available.

When you try to add one of these items to your shopping cart, an unrelated error message is shown and the site prevents you from adding the item to your cart.

This prevents you from paying for an item that is not available. 

Available items can be ordered without any problems.

We are actively working to resolve this error. We sincerely apologise for the inconvenience caused.