Not able to unlock iPhone 4 after pulling battery out

Hi

I have an iPhone 4S with a broken battery, so what I thought, let's take the battery out from my friend's iPhone 4 to look if my iPhone was fine...
I should have checked first if they both have the same battery, they don't...
So I install the battery back in the iPhone 4, the phone starts up perfectly until I have to give the simlock, I can't get passed that.
Did I mess something up?
This is quite urgent, every little help is appreciated

Thanks in advance

Lorenz