I've installed the latest version of DevDemons Forms(3.3.5)
When I navigate to the index page of the Control Panel I'll get the following error.
A PHP Error was encountered
Message: Object of class EE_Session could not be converted to string
Line Number: 240
I also found a bug report on the Ellislab website related to this problem https://support.ellislab.com/bugs/detail/19469