I guess you're right sambob.
The error has gone since I updated to Joomla 3.2.2.
Also the file /public_html/libraries/joomla/application/router.php isn't present anymore after the update.

I have this error too (Joomla 3.2.1 and JoomSEF 4.5.1):
PHP Fatal error: Unsupported operand types in /home/example/public_html/libraries/joomla/application/router.php on line 182

This is on line 182 in router.php: $vars += $this->_parseSefRoute($uri);

Addition:
When clicking on the menu item the result is "no articles found"

After the JoomSEF update to version 4.5.1 the Joomla tags sidemenu isn't working anymore.
All menu items go to http://websiteurl/first-tag/root

In the JoomSEF manage SEF url's section:
index.php?option=com_tags&id=1&layout=list&tag_list_language_filter=&view=tag&Itemid=706
becomes tag/root

Does someone know how to solve this?
OR
Can this be undone in a new version of JoomSEF?

Help would be much appreciated.