Submit Button missing in Adobe Reader XI

Hi.

I have designed an interactive PDF using Adobe LiveCycle.

I have distributed the form and I am collecting responses through my adobe.com ID.

This has worked perfectly well for my customers using Adobe Reader 8 - 10, however with Reader XI the "Submit Form" button seems to be missing from the navigation pane.

This is how the bar looks in Reader 10:

This is how the bar looks in Reader XI:

Can anyone help with this please? I have looked through the forums to no avail.

Thanks

Stuart