Can't Hide Troops in Woods

During the last several battles, the game has not allowed me to hide troops in the woods (you know, when the troops go into that crouch position). I used to be be able to, but suddenly can't. Any suggestions?

I implemented the suggestion provided by a good samaritan on the NTW forum regarding Verifying the Integrity, but it did not improve matters, at least not immediately. However, I fiddled with several other aspects of the computer, such as restoring to an earlier point in time and having Microsoft re-upload the last 15 updates for Windows 7. The last thing I did was to up the graphics to the "High" level. After that, I can now pick berries in the woods to my hearts' content without the enemy being the wiser. In short, I don't exactly know what the remedy was, but the patient has improved considerably.