Most likely you have several adb version on your computer. You start adb server using one version and then trying to connect to this server using another version. For example - Genymotion has it's own adb and if you start Genymotion emulator and then try to use adb from Android SDK most likely you will have such error (the latest Genymotion which is 2.7.2 has adb version 1.0.32 while the latest Android SDK has adb version 1.0.36).