Photostream not working - two iphones, one itunes account, two icloud accounts

Hello,

My wife and I both have iphones (both 4s). I have had mine for some time and she got hers last week.

We have one itunes account. We have two icloud accounts.

We cannot get shared photostreams to - my phone will not receive invites from hers. It works the other way round though.

All the settings are correct and switched on.

Please don't send me to the FAQ page as I have tried everything on there to no avail

Thanks

Matt