First, you need to understand that 'Pure calendar' and 'Pure Grid calendar' doesn't sync any informations, they just read the phone calendar database.
1. Calendar selection in the stock application
You need to check that you see your missing calendars/events in your phone stock calendar application.
If you don't see a calendar, force the application to sync this calendars :
In Calendar stock application -> Menu key -> More -> My calendars, are all of your calendars listed there, and checked?
If not, have you added them with Calendar -> Menu -> More -> My calenders -> Menu -> Add calendars
Then, wait for sync, and reconfigure the widget to enable the widget display in the calendars selector.
2. Android calendar sync
Be sure Google calendars are synced by Android in phone settings (Android settings -> Sync -> calendar).
Then, wait for sync, and reconfigure the widget to enable the widget display in the calendars selector.
3. Still not seeing calendar events
If your calendars are visibles, but not events (in the stock application), then your phone have a problem to sync those events.
A solution, can be to clear your calendar application cache and data (Android settings -> applications -> manage applications -> all applications -> calendar -> clear cache / clear data).
It clear all your phone data, but keep all your calendar informations in Google server.
Then, you'll have to wait for resync, and go to step 1.
There is well know bugs in Android with Google public calendars (like holidays)… they are sometimes very difficult to sync.
4. Scrollable mode
If you are using the scrollable mode, and if it works WITHOUT scrollable mode, BE SURE you enabled the scrollable mode in the Launcher settings (ADW or LauncherPro).
5. Some particular ROM / device issues
- HTC 2.2 / 2.3 ROM : To show your events in Pure calendar widget, you must choose the same calendar in the HTC Sense calendar widget.
- MyTouch 3G Slide ROM problem of calendar sync conflict with FriendStream, the solution, disable FriendStream background sync