I think you misunderstood. It's not that you cant use DW8 with the extensions, it's that DW 8 has been replaced by newer versions of DW and we cant offer support for it, nor will Adobe.
That being said, did you read my other comment?
Have you installed the 8.0.2 update for DW 8?
eCart 4 was never compatible with DW 8.0.0, you need to install the 8.0.2 update if you have not already.