Thanks Dave,
I did what you described and it works now.
I found 2 aviplug-files: one of 1,07 MB (Vidcap) and one of 584 KB (FileIO). Yours is 550 KB.
I changed the .dll file in the FileIO folder and it works now. I did not change the .dll file in the Vidcap folder.
Pretty remarkable I must say.