This is a bug related to Visual Assist and is not specific to Atmel's customized version of Visual Studio. The root cause is a corrupted .suo file (.atsuo in AS). Closing the program and deleting the .suo/.atsuo file from your solution folder will fix the problem. I don't know what the file is used for, but it will be regenerated the next time you open the solution. You can also disable Visual Assist, which disables a lot of helpful features, but it's good for temporary relief. The problem also isn't specific to the dot character, I've seen it crop up with opening parentheses and brackets as well.