'Exception' with message 'Item (Mage_Catalog_Model_Product) with the same id "X" already exists

[Virtual Brick]

On a client's store, getting this exception on all category and product pages (only in one store in the multistore)

'Exception' with message 'Item (Mage_Catalog_Model_Product) with the same id "2233" already exist' in /home/cji/public_html/lib/Varien/Data/Collection.php:373

Always with the same product ID, regardless of the product page loaded.

[Tom Robertshaw]

Can you trace where the error is coming from? Is the message cached on every page load or does the error actually occur on every page load? It doesn't look like something that should be happening on just page load. It looks like a problem with updating products or adding to cart perhaps.

[Virtual Brick]

Sorry, It's been a while, I don't have further details now. 

I had to remove 3 products from being available in one of the stores, which solved the issue. Later on we added them back and the issue did not return (so far).