John M - Thanks for the assist! :)
Grif -
An action sequence error indicates an error with a specific action on the screen. In your case it is action #1. You said this happens when you select an estimate, am I safe to assume this is on the select link in the grid of existing estimates (the grid on the left of the screen)? If so, then action #1 in that action set sets the "Activce Record ID for Screen". In other words this selects the estimate to look at. Here's a screen shot of how it should look like:
Are you seeing something different? Is it a different object this is happening on?
- Adam