I ended up finding a post that had some clues.
Basically, on the magento connect page, it says it is compatible with 1.6 and 1.7, but the latest version (1.7) is not actually compatible with 1.6.
You need to click on release notes and find a previous version that is compatible with 1.6
I uninstalled the original one, and installed the new one, and now I can edit products again.
Also, it retained the 4000-odd products that I had added with the old version which was very nice.
I hope that helps…