I had a similar problem. I don’t know if it was identical to yours, but I was told to install this. After installation, Engrampa started behaving itself with various archives it had previously complained about. So, i am guessing Engrampa must be able to make use of unrar:
sudo apt-get install unrar
As I said, I don’t know if it’s related to your problem, but it shouldn’t hurt to install it and see (unrar is used to process rar and zip files)