I too am having the same problem (capture of error dialog attached).
I have uninstalled all 19 of my WebAssist extensions and reinstalled. I did not uninstall extensions from other sources. This did not resolve the issue. Unfortunately, it takes a lot of time to uninstall and re-install extensions. I hoping there is a solution that will not require me to do this again.
Using "Set Cookie Values" works.
When I access "Set Session Values" it launches the "eCart" activation screen.