Report Paths Issue

I have a report on a server under a folder.  In setting up the ReportViewer control, I set the report path to "[folder name]/[report name]".  When I ran this, I got the following exception

The path must be less than 260 characters long and must not start with slash

It turned out that the path in this instance must start with a slash. "/[folder name]/[report name]"

Is this a requirement only when the report is in a sub-folder, or is the exception text wrong