Blackberry calendar transfer issue

[Dick Dastardly]

Anyone able to help me understand why after a month of working perfectly my Pearl and Outlook are now not playing nice? If I put entries into my Outlook calendar they transfer to the BB but anything in the BB won't transfer into Outlook and it even looks like it's deleting entries from Outlook as the laptop calendar is now empty. I haven't fiddled with any of the settings to make this happen and can't see any obvious switch/fix now that I've looked.

Not the end of the world but if someone calls me on my mobile the only access I have to my calendar is pressed against my ear.