I've experienced this error from both the project page and the home page. Trying to submit two next actions in a row doesn't work. The first gets submitted fine, but "An error occurred on the server" is shown upon trying to submit the second. If I reload the page, it will work properly again. Here's the relevant portion of production.log, showing the first, successful submit and the second, unsuccessful one directly thereafter:

Processing TodoController#add_item (for 127.0.0.1 at 2006-03-15 11:15:57) [POST]
  Parameters: {"action"=>"add_item", "todo"=>{"context_id"=>"1", "project_id"=>"7", "notes"=>"", "description"=>"Use pictures from flier??", "due"=>""}, "controller"=>"todo"}
Rendering todo/add_item
Completed in 0.55939 (1 reqs/sec) | Rendering: 0.02285 (4%) | DB: 0.12051 (21%) | 200 OK "TodoController#add_item (for 127.0.0.1 at 2006-03-15 11:16:46) [POST":http://localhost/todo/add_item]


Processing
  Parameters: {"action"=>"add_item", "todo"=>{"context_id"=>"", "project_id"=>"", "notes"=>"put in site", "description"=>"copy stony brook map and put a circle on it", "due"=>""}, "controller"=>"todo"}
Rendering todo/error
Completed in 0.45749 (2 reqs/sec) | Rendering: 0.00282 (0%) | DB: 0.08744 (19%) | 200 OK "":http://localhost/todo/add_item

The curious thing, and possibly the source of the bug, is that the second submit shows a blank context_id and project_id, yet I actually had them selected. I have gone back and verified this: I can have both items selected, but they come through blank.

By the way, I'm running 1.04, but that's not in the options for versions.