I forgot my local backup password to unlock the iPhone backup file I just received my new iPhone from Apple after I had my old one changed due to it being a rather bad specimen. Now I'm occurring a rather irritating problem, as I connected my iPhone with my iTunes to back up my last iPhone settings etc. it asks me to enter a password I never remember entering myself.

All my important contacts, notes etc. are on my last backup and I am not happy just starting "from the start". So I badly need to enter the password to do the backup.  

I have already searched for some knowledge, but it's useless due to the fact, I have a PC. I know there are ways to see the password with a Mac, but have not yet a solution to figure out the password with a PC. I have tried randomly some numbers, my previous passcode, my password for the SIM-card, nothing. As I also understood, the password has to be a number code from 0000 or 1111 to 9999.
I would be really glad if someone figured this out and let us know, who are occurring this same, rather an irritating problem.
Try using your iTunes password that you use to log into the iTunes store worked for me, after iTunes decided that my backup was encrypted even though I didn't select it.