There is no reported problem using NJStar Communicator v3 on Windows 7/8/10.
[Old Info] In the new version of Google's Gmail, there are some problems for NJStar Communicator 2.75 to input directly into Gmail message box. The problem is there because new Gmail message box does not process windows unicode input messages correctly.
There are two solutions to work around this problem before Google fix the bug.
1. Change NJStar Communicator v2.75 IME settings to enable the option
[ x ] Input CJK text to target window via Clipboard.
2. Use Gmail old version. You can find the 'old version' link at very bottom of your Gmail account, or you can click the foloowing link to start the old version UI.