I am having similar problems, connecting my X51V to my Sony Ericson K750i.
They see each other, and for a secure connection I fill in two identical codes, but when trying to transfer pictures to my X51V, my phone says he can't connect.
Connecting my X51V to my BT GPS was easy, but not to my phone!!
I can send data from my Dell to my phone, but not the other way around

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Is this something that could be solved wit the BT stack I read about? I am reluctant to install it, it looks like an advanced user option..