Metacat

If you click the Register Data menu link without being logged in, it returns a page of registration instructions. Under Step 4 is a hyperlink to "ESA Data Registry Form". Clicking it produces a blank page, I imagine because the application context 'esa' is missing from the URL:
http://data.esa.org/cgi-bin/register-dataset.cgi?cfg=esa

It's not a particularly useful or important link in any case (just returning the same page), but it at least shouldn't return a blank page.