Changed Apple ID is not working with the appstore

Question

I have 2 iPads. Upon updating to iOS 6 I've been experiencing the following problems:
On iPad number 1: My Apple ID works from the settings menu, however when loading into the appstore, it keeps on asking me for a password of an old apple ID that I do not use anymore and I've got no idea how to change this.
On iPad number 2: I moved over all of my apps from first iPad to my second one via the iCloud backup. However any apps purchased on my first iPad, i cannot make in-purchases for on the iPad number 2 as it says the Apple ID I purchased the app on is different from the one currently in use.
Please could anyone help me?
Many thanks!

Answer 1

I have the exact same problem as "Jan Olsen 1"
I sent them feedback:
"I was given a $25 iTunes gift card. 
When trying to log on to my account, my password didn't work (though I entered the correct password THREE TIMES). 
I requested help changing the password through an e-mail. Went through the process, changed the password.
I successfully logged on to my account and entered the gift card information and was given a $25 credit.
When I tried to buy mp3s, I was asked to enter my password - AGAIN. 
I got one of the following messages each time I tried to enter my NEW password:
'We could not complete your iTunes Store request. An unknown error occurred (5002).
There was an error in the iTunes Store. Please try again later.'
or
'Verification is required.
You must enter your AppleID and password, click Billing Info, and verify your payment information in order to make purchases.
The Apple ID you entered couldn't be found or your password was incorrect. Please try again.'
Don't know where to go from here."
And then, just to log on to this forum, I had to enter my AppleID TWICE! Once, then again to verify my AppleID!
Ridiculous! Frustrating!