Thanks Alex,
The 'Rename all tools' function is described in the 'Tool numbering and naming' of this page...
http://cambamcnc.com/doc/plus/cam/ToolLibrary.htmI will look into making the error message less ugly, perhaps just a log message warning and internally make sure the generated name is unique (such as by appending the tool index).
Rename all tools should also be changed to not do anything if there is no 'Tool Name Format' value set.
And while we are at it, I think a confirmation 'This will rename all your tools' would be friendly.
The lathe tool library is a bit odd in that none of the tool properties really identify what the tool is, so it is best to manually set the tool names for lathe tools in the current design.
Thank you for pointing this out, I have added this to the TODO list.