Weird calendar sync'ing issue - entries have disappeared on Gmail/web and phone can't sync

[Guest BillBong]

I've got 2 calendars running on my Gmail account (say A and B) and I use a calendar widget that shows the entries which was has all been running well and sync'ing between the phone and gmail without any problem. Today, the circular sync'ing icon in the taskbar has been running continuously which is unusual and if I go to Settings>Accounts>Sync, it's just spinning against the calendar option. I've tried rebooting, switching the auto sync on/off (for both background and auto sync) but it's still running.

I've just logged onto my Gmail account and all the calendar entries for calendar "B" have disappeared on the web calendar but they do still show on my phone calendar widget (calendar A is OK on both). So it looks like there's a communication issue between the phone trying to send entries to update the web calendar. Has anyone come across this before or is there something on Gmail that I need to reset to get things back to normal?

(IMAP is enabled)

Thanks for any tips