Internal compile error.See the console log for more information??

dude had the same problem however i know what caused it what i did was i moved my quest script from the scripts folder then placed it somewhere else as soon as i did this it said moving failed i clicked try again then quckily saved it this was my problem as ussally when that message appears it closes down unity which is better however i saved it so i moved the quest script back to where it was originally in the scripts folder then the problem was solved how ever i dont know what your problem could be let me know if this has helped :)

when i write code"sqlconnection conn=new sqlconnection()",the unity put out the error:

Internal compiler error. See the console log for more information. output was: Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly 'System.EnterpriseServices, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies.

i use dotnet 4.0 and i change the system.dll and system.data.dll severl times cann't remove it, now i have no way to defeat it ,please give me help,thanks very much!