This was fixed in 1.2.4 version. Try to update it.

I'm having the exact same issue with a fresh install of 1.2.4. Everything was fine at first. Was in the middle of setting up permissions etc when BAM..I got this error msg

 Message: Can't generate uri for empty controller/action !
 File: /home/razz99h/public_html/in-rpc/ow_core/default_route.php
 Line: 49
etc etc etc...InvalidArgumentException

Found the solution. -exhales relief-..

"WhitewaterDave Aug 8
Message #13
Hi everyone, I'm new. Great software so far.

I had the same problem with adding the "Terms of use" page to the bottom menu. It completely shut down my site. The page is missing or linked incorrectly.
I was able to recover by making a change in the database. It's easy to do if you use phpMyAdmin to administer you database. I'll try to explain.

Back up your database first in case something goes wrong.
Click on the database on the left so it expands the list of table in the database.
Look for the table that has "base_menu_item" in its name and click on it.
Choose "browse" from the tabs at the top so you can view the content of the table.
In the table header, look for "id".
You will probably have to go to the second page of content by clicking the button that has " > " on it.
Locate "411" in the id column.
Click the pencil icon to the left of 411 in the same row. This is for editing the record.
Locate the word "type" in the column "field" in the form.
In the same row, there is a text box on the right side. It will probably say "middle". Change the value to "hidden" without the quotes.
On the bottom right corner of the form, click "Go" to commit the new value.
 Your site should be functioning now."

Thank you thank you thank you!!