Using 188.8.131.524 - Vigo, hovering over a change set that has no comment causes the "An error occurred processing your request." message to appear.
It appears that every other change set that has a comment works fine, just not the ones where I did a merge and didn't add a comment, though clicking on the CS and viewing the properties has the correct info.
BranchExplorer-error.PNG 29.76KB 9 downloads
The error goes away if I manually add a comment in the properties pane and save it for that change set.