warning message in product description block/tab

I have set up a related products tab using the "product " option.

This produces a message by the product

Warning: strpos() expects parameter 1 to be string, array given in C:\xampp\htdocs\cscart\core\templater_plugins\modifier.escape.php on line 24

It does the same if I create a block with the same selections.

I thought it might have been a template problem but it does the same with the basic skin.

Any ideas as to what is causing this?

It is fairly crucial as I need the ability to show the full description and add to cart button on the same page for the matching product