The GraphViz extension does actually not work on windows at my side, this one works perfect. In the QuickGV body php you have some constants for the dot.exe path, may you can add them to the local settings php? I hope you keep this cool extension up :D Thanks
Topic on Extension talk:QuickGV/Flow
I hope this extension be a zero-config and cross platform extension.
If you need to use QuickGV in an unusual environment, please give me a suggestion.