Why can't I select a To Do item in iCal?

I am having a seriously annoying problem trying to select a to do item in iCal. This is what is happening:

1/ in iCal I have this month's view showing September
2/ I go to the To-Do side bar and scroll down to a task that is due tomorrow.
3/ On clicking on it, an item in July gets selected and the month in the calendar window changes to July.
4/ Some functions seem to work properly so for example when I do Command-T, today's date does not get selected UNLESS in click in the calendar view and then do Command-T. However the month and date does show up in the mini calendar view in the left window. All very confusing.

This happens for any random item, not just for tomorrows.

I have a sneaky suspicion this might have something to do with clearing a cache or some other software fiddle but have no idea what. Any suggestions warmly accepted.

Thanks