Is a dollar bill with two different Serial Number letters valuable?

Question:

Is a dollar bill with two different Serial Number letters valuable?

I found a dollar billon which the serial number letters are different from each other but I found another one on which they are the same. So is the one with different letters more valuable or rare or something? The letter on the begining of the serial number is F and at the end is M, but on my other dollar both of the letters are A's (similar).

Best Answer - Chosen by Asker:

an error.... and worth money