What causes this error in 0x51.
0x203: Wrong product

It has done this sometimes using a valid w3 key with client as WAR3, any ideas?

Supply a valid product

Did you reverse the product string?

[quote author=Topaz link=topic=12434.msg123106#msg123106 date=1123204309]
Did you reverse the product string?
[/quote]

There are no such strings that are to be reversed

DWORD.

[quote author=Topaz link=topic=12434.msg123132#msg123132 date=1123214018]
DWORD.
[/quote]

[quote author=google define: DWORD]
Definitions of  DWORD on the Web:

    * Double word, ie 4 bytes on x86.
      www.kernelhacking.org/docs/kernelhacking-HOWTO/indexs17.html

    * Double word. A data element that is 2 words, 4 bytes, or 32 bits in size.
      www.ti.com/sc/docs/products/msp/intrface/usb/terms.htm

    * A portion of memory, usually a variable, which has a length of four bytes. The term dword is given to anything which is four bytes in length. Literally, a dword is a "double word." Back
      www.pietschsoft.com/programming/vbapi/ref/glossary.html
[/quote]

I don't see string nor reverse.

If your key is indeed valid then you're either sending SID_AUTH_CHECK incorrectly or your CD-Key decoding algorithims are flawed.  Yes, it's a vague answer, but it was also a vague question.

Recall how you have to send WAR3 as 3RAW to battle.net? Same thing with STAR -> RATS.

That's only if you decide to use the trick to get around sending a DWORD by sending a non null terminated string reversed (which ends up a DWORD)

[quote author=Warrior link=topic=12434.msg123140#msg123140 date=1123217113]
That's only if you decide to use the trick to get around sending a DWORD by sending a non null terminated string reversed (which ends up a DWORD)
[/quote]

People who consider a "non-null terminated string" to be a valid datatype shouldn't expect to make a working bot.

Let's not go through this topic over and over again ad nauseam.

Topaz, read Sizes & Types in BnetDocs and do some searches in the forum.