Check if you have the right FTDI drivers installed and than restart the computer 
It worked for me. Had the exact same error: seeeduino on Vista (i assume you have Vista too). Have to run ***.bat, the arduino.exe wouln'd start.
Now it works great. I tested a servo and a blinking LED, but have to search for some software examples of a servo and LCD display driving that doesn't use delay() function, since i want to display different data including time in real time on the LCD.
Regards, Sandi