:JavaRename does not work most of the time, but sometimes it works

I enter the command like this :JavaRename In the console at the bottom I am asked to type 'e' to confirm my renaming of this class. I type 'e' and press 'enter'. Most of the time nothing happens, without any message explaining that something the renaming cannot be done because of reason x. Other times it works fine. Anybody know what might be going on or where I could look to find the problem?