Search your logs for the exception number. If you don't know where the logs are you, ask your host.

The exception number is not telling about a specific error having occured. The number is a timestamp telling WHEN the error occured. The error is logged in the server logs (together with the exception number). To find out more about what the reason for the error is you would have to check the log files (Apache log and/or php log).

I could be wrong, on the surface it looks like you would have to edit /mod/aalborg_theme/views/default/page/elements/header.php

I'm sure if I'm wrong someone will jump in and give you the correct answer.

That is the correct view, but you shouldn't edit it, you can override it in your own plugin.

http://learn.elgg.org/en/1.10/guides/views.html

Coles notes:

Create a plugin (required start.php and manifest.xml)

Create the file: views/default/page/elements/header.php

Enable your plugin, make sure it is below aalborg