VC for NW 7.4 - strange behavior

Hi,

after a long time our company's Portal installation got updated to 7.4, and I have to check the VC content I created years ago.

The content is still running, but the Visual Composer behaves strange and erroneous.

I'd like to illustrate this behavior with the Create New Model dialog:

On clicking the toolbar button, this dialog is shown. Interaction is only possible on the literal "Cancel", clicking there closes the dialog.

This dialog is shown once, after closing it, it won't open until a new logon to the Visual Composer.

I'm Using Internet Explorer 11, and Visual Composer for NetWeaver 7.4 SPS 07.

Did anyone face similar problems, and could provide a solution for me?

Is there a guidance, that helps me to check that my installation and configuration is proper?

Thanks, Stephan