SQL Error 18456 State 28000

Hi

I recently came accross a machine that had me confused... The connection from this machine to our production SQL server refused to work... here is what I tested:

Before I start, here are our actors:
* Machine A - The client that won't connect
* Machine B - My Dev machine
* SQL A - Our Production SQL server
* SQL B - Our dev server
* Login A - The login of the regular user of Machine A
* Login B - My admin login
* Profile A - The user's profile
* Profile B - my windows profile

So, to the test:
1. Profile A - Machine A to SQL A using Login A... Failed
2. Profile A - Machine A to SQL A using the "sa" account... Failed
3. Profile A - Machine A to SQL B... Works 100%
4. Profile B - Machine A to SQL A using Login A... Success
5. Profile B - Machine A to SQL A using the "sa" account... Failed
6. Profile B - Machine A to SQL B... Works 100%
7. Profile A - Machine B to SQL A using Login A... Works 100%
8. Profile A - Machine B to SQL A using the "sa" account... Works 100%
9. Profile A - Machine B to SQL B... Works 100%

So, the credentials are correct. It's only when you connect Machine A to SQL A that there is an error.

Lots of googling revealed a lot of people saying stuff like "Check your passwords"... NOT HELPFUL!!! At this point, if you hadn't checked the passwords, you deserve a kick in the patootie!!

So, I asked a DBA what he tought, and he suggested I check the SQL Network Client Configuration. There was an alias to the server... it was 100% correct (the right IP, and the right details), but I deleted it anyway...

LO AND BEHOLD, IT WORKED!!!

Go figure!!!