The iCal on OSX 10.7.5 should be version 5, not 4.
Is the iCal application in your Applications folder version 5.0.3? (You can check this without opening it by Control-Clicking the iCal application in the Finder and selecting 'Get Info' from the contextual menu.)
Thanks for your reply. I looked in the Applications folder and it says I have version 5.0.3 but when I click on the iCal icon on my desktop it won't open and says that I have version 4.0.4 and that it won't work.
Any other suggestions on what to do?