It could be something simple as your account settings.

Lets check if your password is missing from the CalDAV account setup.

(iCal->Preferences->Accounts->[email protected] CalDav->Account Information->password). 

Enter your password even it it shows something there just to make sure it is correct one.

then Go Offline then Go Online under the Calendar menu and it immediately synced up.

Also go to the Google calender settings and make sure sync is enabled.