Yea, I originally built the post slug addon for use with Pixelpost v1.5. So obviously, it doesn't work with the latest v1.7.1
And eventually, when I upgrade my photoblog to v1.7.1, I will be releasing a new version of the Post Slug addon as well.
However, in the mean time, using a program such as WinMerge may help to you get it working. http://winmerge.org/