favicon.ico - 404 also present?

I have been searching the net for learning about this file but I am still missing some information:

how big is too big?

I joined two .ico files one 16x16 one 32x32 pixels and the resulting file is now 3638 bytes big.

Sometimes in the logfiles I see 404 errors concerning my favicon.ico. That is not supposed to be so here are my questions:

is it too big and to which mode do I have to chmode it.

That does seem awfully big. Mine is only 318 bytes.

16X16 is desired: http://www.favicon.com/#1-12
You can also maybe design a new one to check it out here: http://www.favicon.co.uk

thx for the reply,

after a thorough examination I found that during a conversion the colors were changed from 16 colors to 24bit. changed it back and now its around 1300bytes. Which sounds acceptable for a two images .ico (remember I have two images 16x16 and 32x32 in the one .ico file)