Hey guys,
Finally managed to download the whole blockchain on the new wallet.
Everything looks fine up to the moment in which I replace the private key with my old wallet.
I get the next error:
Runtime Error
This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
So here I am asking for more information from support team

unfortunately errors like that give me little or no information XD
by replace the private key, you mean load it up with a new wallet.dat? or importprivkey from console?
I meant load it up with my older wallet.dat, where my coins are stored.