x201 & bluetooth & Microsoft mice: connectivity problem

[JPH]

I absolutely love my x201 but one thing that is bothering me is that with my MS mice occasionally the BT connection is lost. I usually use a Notebook Presenter Mouse 8000 but my 2 backups also suffer from the same problem (another presenter 8000 and a Mouse 5000). I am running all the latest drivers and all is OK. Sometimes I can be at it for a couple of hours before the BT connection drops, sometimes it happens after 30 minutes. I turn my mouse off and on and usually it is recognised again but sometimes the ultimate recourse is to reboot the laptop. UltraNav operations are unaffected.
Any clue anyone? I am tired of losing connection in the middle of a presentation - it is driving me nuts!

Edit: FWIW I am running W7Pro x86 on the x201; the problem does not occur with the XP on my T61 or my T400