The access to C:/Users//Documents//Temp/Assembly-CSharp.dll.mdb is denied.
My OS is Windows 8.1 & the Unity version is 4.5.3f3.
PLEASE HELP ME I CANT’T WRITE ANY C# CODE!!!
If this is happening while you have the debugger attached, have a look at this patch. If your debugger is not attached, do as Graham says, the exact steps depend on your antivirus software, look for “exclusions by path” or “white lists”, etc.