How to upload an XML file to wishlist in bricklink I am trying to upload an XML file with my brick wishlist to BrickLink. 
However, even if I follow the instructions on the webpage, it never seems to find the product in the catalogue. If I manually use the search bar to search it in the catalogue however, it will always find it.

I have no idea what is wrong.

The help says:

&lt;INVENTORY&gt;
    &lt;ITEM&gt;
        &lt;ITEMTYPE&gt;P&lt;/ITEMTYPE&gt;
        &lt;ITEMID&gt;3622&lt;/ITEMID&gt; 
        &lt;COLOR&gt;11&lt;/COLOR&gt; 
    &lt;/ITEM&gt;
&lt;/INVENTORY&gt;


If I change that to:

&lt;INVENTORY&gt;
    &lt;ITEM&gt;
        &lt;ITEMTYPE&gt;P&lt;/ITEMTYPE&gt;
        &lt;ITEMID&gt;3062&lt;/ITEMID&gt; 
        &lt;COLOR&gt;23&lt;/COLOR&gt; 
    &lt;/ITEM&gt;
&lt;/INVENTORY&gt;


It doesn't work. However it does exist: http://www.bricklink.com/catalogItem.asp?P=3062b&amp;ccName=306223

and that with the 6 Digit IDs. What about the other ID types, the ones that can not be broken into colour/ID? e.g.: 4211425

How can I upload my list to Bricklink?
Bricklink is correct - 3062 does not exist. Your link shows 3062b, which DOES exist (Don't ask me why the base number does not exist though :) ). So if you change your XML to

    &lt;INVENTORY&gt;
        &lt;ITEM&gt;
            &lt;ITEMTYPE&gt;P&lt;/ITEMTYPE&gt;
            &lt;ITEMID&gt;3062b&lt;/ITEMID&gt; 
            &lt;COLOR&gt;23&lt;/COLOR&gt; 
        &lt;/ITEM&gt; 
    &lt;/INVENTORY&gt;


It should load.

I do not know the answer to the second part of your question: 4211425 translates to ITEMID 3460 in color White, and the Catalog knows this, but the wanted list does not :(.