For the latest Slicer documentation, visit the 4.10 page.
The error log dialog is accessible from View -> Error Log or via the Ctrl+0 shortcut.
All the outputs (errors, warnings, messages, information) generated by the application and modules are gathered in this dialog. This readout is useful for reporting bugs or usability problems back to the Slicer Development Team.
The dialog is split in 2 parts, the top section is a digest listing of outputs that are merged by type and time. If multiple errors are output within a short period (<1ms) of time from a given component, they will show up as 1 item in the digest list. The bottom section of the dialog prints all the details of the digest list. Selecting one or multiple items in the digest list, results in the printing of all merged lines in the detailed bottom list.
When reporting a bug on the mailing list or in the bug tracker, it is valuable information to include a dump of the errors that appear in the Error Log dialog.