SP2010 - Error copying "Globally Reusable Workflows" at a sub-site level...

Customer of mine was an having annoying issue on random SP2010 farms trying to copy the "Approval - SharePoint 2010" Globally Reusable Workflow... and other OOTB workflows at subsite level...

On some farms it would work great and other very similar farms, it would error out...

After doing some research online, they were getting the famous "The server could not complete your request" with the blank Details pane when trying to copy an OOTB workflow...

Running a Fiddler 2 trace while trying to copy the workflow via SharePoint Designer showed that URLs ending inĀ  ".rules" & ".xoml" were being blocked.

Looking at IIS 7.5 under Request Filtering, both ".rules" & ".xoml" were set to false under enabled.

After I deleted both entries, I was able to copy the OOTB workflows at a subsite level.

You would also need to re-add them via "Allow File Name Extension" in the Request Filtering area, if you have "Allow unlisted file name extensions" unchecked.