You may see the error "The specified path, file name, or both are too long. The fully qualified file name must be less than 260 characters, and the directory name must be less than 248 characters," under the following circumstances:
This is not a problem with .NET Reflector, or any of its add-ins, but is rather a limitation of the Windows operating system:
http://msdn.microsoft.com/en-us/library/aa365247(VS.85).aspx#maximum_path_length
The solution is to either move the assembly you're trying to open into a directory with a shorter path-i.e., that is less deeply nested in the directory hierarchy-or to export source code to a directory with a shorter path.
In case you're interested, the pros and cons of the 260 character path limit on Windows are discussed in these posts:
http://www.codinghorror.com/blog/archives/000729.html
http://eamon.nerbonne.org/2006/11/why-maximum-path-lengths-are-bad-idea.html