My shop has been up and running for few weeks now. Today I wanted to add new product and here's what happened. I went admin/configure/categories/products and I see the following error:

1 Can't create/write to file '/tmp/#sql_d3d_0.MYI' (Errcode: 28)
[select c.categories_id, cd.categories_name, cd.categories_description, c.categories_image, c.parent_id, c.sort_order, c.date_added, c.last_modified, c.categories_status from categories c, categories_description cd where c.parent_id = '0' and c.categories_id = cd.categories_id and cd.language_id = '1' order by c.sort_order, cd.categories_name]
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I checked my online shop to see how things are there and I see same code in the categories (I can see subcategories, but if I press on them I get same message). No products to view. here's my site just in case:

Zen cart version 1.3.8b , and I haven't changed anything like coding, I added new products just yesterday and it was fine.