This is a bug with DW, because it remembers all the windows you have opened the last time you opened DW. After you uninstall Theme-it browse to this location:
C:\Users\<Your UserName>\AppData\Roaming\Adobe\Dreamweaver CS4\en_US\Configuration\Workspace
And delete the Designer.xml, and then open DW again. This should clear the error.
In regard to the other issue you had, we released a dot release 1.0.1 and the fix to your issue should be included in that build.
Let me know if you still have any other questions.