All Script Error when upgrading to Unity4

I'm just upgrading my project that made with Unity3.5 to Unity4. But my script (Javascript) says "The Associated script can not be loaded. Please fix any compile error and assign a new script."

I also check at the Console. and most problem says "Assets/Skipper/Scripts/CORE/GM.js(55,24): BCE0019: 'enabled' is not a member of 'UnityEngine.Cursor'."

While i'm trying to fixing it, MonoDevelop flashing many times (minimize, restore, and Not Responding in every seconds). and then it appears Error while updating status of command: MonoDevelop.Ide.Commands.ProjectCommands.Run.

If this problem can't fixed, i have Unity 3.5 in my computer and backup project, can i just use Unity3.5 and Uninstall Unity4 ?