Fatal error message when sending message

Hello all,
When sending a message with uddeIM 1.7/2009-04-01 I get the following 2 error messages on my screen:

Notice: Trying to get property of non-object in C:\wamp\www\www.vaszuiddrenthe.nl\includes\router.php on line 148

Fatal error: Unsupported operand types in C:\wamp\www\www.vaszuiddrenthe.nl\includes\router.php on line 148

Also when I click on "reaction on this message" the following message appears:

Notice: Trying to get property of non-object in C:\wamp\www\www.vaszuiddrenthe.nl\components\com_uddeim\outbox.php on line 297

Am I doing something wrong in the settings?

Thanks in advance,
regards,
Emiel Kempen

There is a comprehensive section about this error in the FAQ.

In most cases: Create a menu link and when it is already present, check the ItemId if it is correct.