Error while command: service: "ecmascript"

Question

I successfully run locator commands in Firefox, Chrome, and IE, but I have a problem with Opera 12.02 .
This code is the source of the problem:

driver.findElement(By.id("MainContent_txtUserLog")).sendKeys(" [e-mail] "); //entering values to a username field 

The following error appeared in the console:

 com.opera.core.systems.scope.exceptions.CommunicationException: Error on command: service: "ecmascript" commandID: 2 format: 0status:tag: 32 payload: "\n%Unknown error while executing command" 

I'm new to Selenium Webdriver, what am I doing wrong?