General
A first step in troubleshooting any plugin should be to install the Health Check & Troubleshooting plugin. This plugin allows you to view you site as an administrator with all other plugins disabled and using the default theme, while keeping you site fully intact for other visitors. Then you can see if the problem goes away, and enable other plugins one by one to isolate the conflict.
For more information on using this valuable tool, please visit the WordPress documentation.
I upgraded to version 3 and now my events are not appearing
There are several other plugins which use similar names in their calendar CSS. If you use one of these plugins, it might cause your Spiffy events to be hidden from display.
To remove the conflict, try adding this to your CSS:
.spiffy .calnk a span { display: inline-block; }
This conflict was fixed in Version 3.0.3.