Report on Activities

I am trying to create a report based on activities. Every time I try and create or customize a report that is based on any type of activity and I hit save or run it seems like the report module shuts down. I have tried letting it process for a long time but that doesn't help. My report never processes or loads or saves.

Can I run reports and Tasks and Events? Please let me know how I can do this.

Thanks,

John